diff --git a/.issueflows/03-solved-issues/issue181_original.md b/.issueflows/03-solved-issues/issue181_original.md
new file mode 100644
index 0000000..935ea80
--- /dev/null
+++ b/.issueflows/03-solved-issues/issue181_original.md
@@ -0,0 +1,13 @@
+# Issue #181 — turning off mute by group reduces interpretability
+
+Source: https://github.com/cellpy/cellpy-simple-gui/issues/181
+
+Here is an example with mute by group on: (screenshot — cells of one group share
+a colour)
+
+Here is after turning it off: (screenshot — every cell has its own colour)
+
+It is almost impossible to get an impression of what group each cells belong
+to. This is however very important information. Propose to keep cells in the
+same group with the same color also when mute by group is off. Consider option
+for using a gradient within group (saturation).
diff --git a/.issueflows/03-solved-issues/issue181_plan.md b/.issueflows/03-solved-issues/issue181_plan.md
new file mode 100644
index 0000000..cae974a
--- /dev/null
+++ b/.issueflows/03-solved-issues/issue181_plan.md
@@ -0,0 +1,37 @@
+# Plan — #181 keep group colours when "Mute by group" is off
+
+## Findings
+
+- cellpy colours per-cell traces by **group** whenever `group_cells` is on,
+  independent of `group_legend_muting`; muting only decides what goes on
+  `legendgroup` (the group number, or the cell name).
+- The app's own colorway pass (`collect._apply_colorway`, used by the `safe`
+  and `muted` schemes) keys colours by `legendgroup or name`. With muting off
+  that key is the cell name, so every cell gets its own colour — the issue.
+- With muting on, cells of one group are drawn in **identical** colours (cellpy
+  removes the sub-group markers), so the members cannot be told apart either.
+- `library.PALETTE` (= the `safe` scheme) also paints the sidebar swatches by
+  `(group - 1) % len`; the plot used order of appearance instead.
+
+## Approach
+
+Colour by group, shade by member — in both muting modes, for every scheme:
+
+1. `collect.cell_groups(records)` → `{batch key or group name: group}`;
+   `plotting` passes it to `figure_json(cell_groups=…)` for the summary
+   (ungrouped) and the Cycles pane (`per_cycle` layout; `per_cell`/`film`
+   colour by cycle and are left alone).
+2. `_apply_colorway(fig, scheme, cell_groups=…)`: traces are bucketed by group
+   via name / legendgroup lookup. A group's base colour is the scheme colour at
+   `(group - 1) % len` (so `safe` matches the sidebar swatches, and colours
+   stay put when a group disappears) or, for the `cellpy` scheme, the colour
+   cellpy already gave the group. Members of a multi-cell group get a lightness
+   gradient around the base (`_shade_series`, HLS, clamped so nothing goes
+   white/black); singletons keep the base exactly. Ungrouped traces keep the
+   previous order-of-appearance behaviour. Colouring moves ahead of legend
+   truncation in `_restyle` so truncated names cannot collide.
+3. Tests: muting off keeps one hue per group (safe scheme); members of a group
+   get distinct shades of the same hue in both muting modes; `cellpy` scheme
+   shades from cellpy's own group colour; `per_cell` layout untouched; `safe`
+   base colour equals the sidebar swatch.
+4. Design doc (`group-legend-muting.md` / `plot-appearance.md`) + README line.
diff --git a/.issueflows/03-solved-issues/issue181_status.md b/.issueflows/03-solved-issues/issue181_status.md
new file mode 100644
index 0000000..a200b05
--- /dev/null
+++ b/.issueflows/03-solved-issues/issue181_status.md
@@ -0,0 +1,40 @@
+# Status — #181 keep group colours when "Mute by group" is off
+
+- [x] Done
+
+## What was done
+
+- `collect.cell_groups(records)` maps trace names (batch keys and group names)
+  to group ids; `plotting.summary_figure` and `plotting.cycles_figure`
+  (`per_cycle` layout) pass it to `figure_json(cell_groups=…)`.
+- `collect._apply_colorway` buckets per-cell traces by group and paints each
+  group with one hue — the scheme colour at `(group - 1) % len` (so the `safe`
+  scheme matches the sidebar swatches) or, for the `cellpy` scheme, the colour
+  cellpy already gave the group — fanned into lightness shades per member via
+  the new `_shade_series` / `_parse_color` / `_trace_color` / `_paint`
+  helpers. Singletons keep the base colour exactly. Traces outside any group
+  (group averages, `per_cell` facets coloured by cycle) keep the previous
+  order-of-appearance colouring.
+- Colouring now runs before legend truncation in `_restyle`, so truncated
+  names cannot collide.
+- Result is identical with **Mute by group** on or off; muting only decides
+  what a legend click toggles.
+
+## Tests
+
+- `tests/test_core.py` (#181 section): `cell_groups` map, `_shade_series`,
+  summary colours follow groups for every scheme × both muting modes, both
+  muting modes give identical colours, Cycles pane follows groups while
+  `per_cell` stays coloured by cycle, group-average traces keep their swatch
+  colours. Full suite green.
+
+## Docs
+
+- `.issueflows/04-designs-and-guides/plot-appearance.md` and
+  `group-legend-muting.md` updated; README feature line; `llms-full.txt`
+  regenerated.
+
+## Remaining
+
+- Nothing. A saturation (rather than lightness) gradient was considered and
+  rejected: muted base colours lose their identity when desaturated further.
diff --git a/.issueflows/01-current-issues/issue187_original.md b/.issueflows/03-solved-issues/issue187_original.md
similarity index 100%
rename from .issueflows/01-current-issues/issue187_original.md
rename to .issueflows/03-solved-issues/issue187_original.md
diff --git a/.issueflows/01-current-issues/issue187_plan.md b/.issueflows/03-solved-issues/issue187_plan.md
similarity index 100%
rename from .issueflows/01-current-issues/issue187_plan.md
rename to .issueflows/03-solved-issues/issue187_plan.md
diff --git a/.issueflows/01-current-issues/issue187_status.md b/.issueflows/03-solved-issues/issue187_status.md
similarity index 100%
rename from .issueflows/01-current-issues/issue187_status.md
rename to .issueflows/03-solved-issues/issue187_status.md
diff --git a/.issueflows/04-designs-and-guides/group-legend-muting.md b/.issueflows/04-designs-and-guides/group-legend-muting.md
index 99d6040..2926bbf 100644
--- a/.issueflows/04-designs-and-guides/group-legend-muting.md
+++ b/.issueflows/04-designs-and-guides/group-legend-muting.md
@@ -17,6 +17,15 @@ series. The app did not expose the knob.
 - Do not expose a separate `group_cells` checkbox; muting alone is enough.
 - Cell explorer stays out of scope.
 
+## Colours do not depend on muting (#181)
+
+Turning **Mute by group** off used to recolour the figure: the app colorway was
+keyed by Plotly `legendgroup`, which cellpy sets to the group id (muting on) or
+the cell name (muting off), so each cell got its own colour and group identity
+was lost. Since #181 the colorway is keyed by `collect.cell_groups(records)`:
+cells of one group share a hue and differ by lightness, in both muting modes.
+See [`plot-appearance.md`](plot-appearance.md).
+
 ## Alternatives considered
 
 - Hide the control when N/A — rejected; disable + tooltip keeps layout stable.
diff --git a/.issueflows/04-designs-and-guides/plot-appearance.md b/.issueflows/04-designs-and-guides/plot-appearance.md
index 9e520a3..1c9f504 100644
--- a/.issueflows/04-designs-and-guides/plot-appearance.md
+++ b/.issueflows/04-designs-and-guides/plot-appearance.md
@@ -22,6 +22,16 @@ light/dark shell hook.
 - **Persistence:** `localStorage` keys `csg-figure-theme`, `csg-color-scheme`.
   Existing Light/Dark choices in localStorage stay respected.
 - **Cell-list swatches** stay on `PALETTE` and do not follow the plot scheme (v1).
+- **Colour by group, shade by member (#181):** for per-cell traces
+  `_apply_colorway` takes a `cell_groups` map (`collect.cell_groups(records)`,
+  trace name → group id) and paints every group with one hue — scheme colour
+  index `(group - 1)` (so `safe` matches the sidebar swatches) or, for the
+  `cellpy` scheme, the colour cellpy already gave the group — fanned into
+  lightness shades per member (`_shade_series`, HLS lightness ±0.11 per
+  member, capped at ±0.275). The result is identical whether **Mute by
+  group** is on or off; muting only decides what a legend click toggles.
+  Group-average traces (`group_cells=False`) and `per_cell` cycle facets
+  (coloured by cycle) are left to the plain order-of-appearance pass.
 - Keep legend truncation + colorway in app `_restyle`. As of cellpy
   **2.1.1.post4** (#801), paper/plot/font colors and panel height go through
   `layout_updates` / `height_per_panel` (`collect._inject_app_chrome`); facet
diff --git a/README.md b/README.md
index 201f5f7..6c6460b 100644
--- a/README.md
+++ b/README.md
@@ -120,7 +120,7 @@
 - **Cell list** — rename, group, name the groups, select, filter, sort, remove.
 - **Projects** — save and reopen the loaded cells, grouping, group names, labels, and selection. Unsaved edits show as `name*`.
 - **Export** — CSV, Excel, Parquet, JSON; figures as PNG, SVG, PDF.
-- **Light and dark themes.**
+- **Light and dark themes.** Plot colour schemes colour by group (one hue per group, a shade per cell) whether or not legend muting is by group.
 - **Background loading** with progress.
 - **Instruments** from the installed cellpy, including each loader's sub-models.
 - **Developer mode** — every summary family cellpy registers, raw traces, diagnostics (`run --dev`).
diff --git a/llms-full.txt b/llms-full.txt
index 96b2780..604a596 100644
--- a/llms-full.txt
+++ b/llms-full.txt
@@ -132,7 +132,7 @@ FILE: README.md
 - **Cell list** — rename, group, name the groups, select, filter, sort, remove.
 - **Projects** — save and reopen the loaded cells, grouping, group names, labels, and selection. Unsaved edits show as `name*`.
 - **Export** — CSV, Excel, Parquet, JSON; figures as PNG, SVG, PDF.
-- **Light and dark themes.**
+- **Light and dark themes.** Plot colour schemes colour by group (one hue per group, a shade per cell) whether or not legend muting is by group.
 - **Background loading** with progress.
 - **Instruments** from the installed cellpy, including each loader's sub-models.
 - **Developer mode** — every summary family cellpy registers, raw traces, diagnostics (`run --dev`).
diff --git a/src/cellpy_simple_gui/core/collect.py b/src/cellpy_simple_gui/core/collect.py
index c33595a..514e6a1 100644
--- a/src/cellpy_simple_gui/core/collect.py
+++ b/src/cellpy_simple_gui/core/collect.py
@@ -12,6 +12,7 @@
 
 from __future__ import annotations
 
+import colorsys
 import io
 import logging
 
@@ -109,6 +110,20 @@ def group_titles(records: list[CellRecord]) -> dict[str, str]:
     return {str(rec.group): rec.group_label for rec in records if rec.group_label}
 
 
+def cell_groups(records: list[CellRecord]) -> dict[str, int]:
+    """Legend key → group number, for colouring traces by group (#181).
+
+    Per-cell traces are named after the batch key; group-averaged traces are
+    named after the group (``group_name``). Both resolve here so the colour
+    pass can find a trace's group whatever ``legendgroup`` carries.
+    """
+    out: dict[str, int] = {}
+    for key, rec in zip(batch_keys(records), records, strict=True):
+        out[key] = rec.group
+        out.setdefault(rec.group_name(), rec.group)
+    return out
+
+
 def _apply_group_titles(fig, titles: dict[str, str]) -> None:
     for tr in fig.data:
         group = getattr(tr, "legendgroup", None)
@@ -878,6 +893,7 @@ def figure_json(
     overlay: bool = False,
     warnings: list[str] | None = None,
     group_titles: dict[str, str] | None = None,
+    cell_groups: dict[str, int] | None = None,
     **plot_kwargs,
 ) -> str:
     # spread (mean ± std band) only makes sense once actually group-averaged.
@@ -905,7 +921,12 @@ def figure_json(
             fig = _overlay_facets(
                 fig, height=opts["height_per_panel"] + opts["figure_border_height"]
             )
-        _restyle(fig, figure_theme=figure_theme, color_scheme=color_scheme)
+        _restyle(
+            fig,
+            figure_theme=figure_theme,
+            color_scheme=color_scheme,
+            cell_groups=cell_groups,
+        )
         if group_titles and not is_grouped(collection):
             _apply_group_titles(fig, group_titles)
         if y_ranges:
@@ -1366,30 +1387,132 @@ def _hex_to_rgba(color: str, alpha: float = 0.28) -> str:
     return color
 
 
-def _apply_colorway(fig, color_scheme: str) -> None:
-    """Cycle a discrete colorway across legend series (name / legendgroup)."""
+def _parse_color(color) -> tuple[int, int, int] | None:
+    """``#rrggbb`` / ``rgb(…)`` / ``rgba(…)`` → ``(r, g, b)``; None when unknown."""
+    if not isinstance(color, str):
+        return None
+    c = color.strip()
+    try:
+        if c.startswith("#") and len(c) == 7:
+            return tuple(int(c[i : i + 2], 16) for i in (1, 3, 5))  # type: ignore[return-value]
+        if c.startswith("rgb"):
+            parts = c[c.index("(") + 1 : c.rindex(")")].split(",")[:3]
+            return tuple(int(float(p)) for p in parts)  # type: ignore[return-value]
+    except (ValueError, IndexError):
+        return None
+    return None
+
+
+def _shade_series(base: str, n: int) -> list[str]:
+    """``n`` shades of ``base`` — same hue, lightness spread around it (#181).
+
+    One member keeps the base colour exactly, so a singleton group matches
+    its sidebar swatch. Several members fan out from darker to lighter, the
+    span growing with the count and clamped so no shade turns black or white.
+    """
+    if n <= 1:
+        return [base]
+    rgb = _parse_color(base)
+    if rgb is None:
+        return [base] * n
+    h, lum, sat = colorsys.rgb_to_hls(*(v / 255 for v in rgb))
+    span = min(0.55, 0.22 * (n - 1))
+    out: list[str] = []
+    for i in range(n):
+        t = i / (n - 1)
+        l_i = min(0.86, max(0.2, lum + (t - 0.5) * span))
+        r, g, b = colorsys.hls_to_rgb(h, l_i, sat)
+        out.append(f"#{round(r * 255):02x}{round(g * 255):02x}{round(b * 255):02x}")
+    return out
+
+
+def _trace_color(tr) -> str | None:
+    line = getattr(tr, "line", None)
+    color = getattr(line, "color", None) if line is not None else None
+    if isinstance(color, str):
+        return color
+    marker = getattr(tr, "marker", None)
+    color = getattr(marker, "color", None) if marker is not None else None
+    return color if isinstance(color, str) else None
+
+
+def _paint(tr, color: str) -> None:
+    try:
+        if getattr(tr, "line", None) is not None:
+            tr.line.color = color
+        if getattr(tr, "marker", None) is not None:
+            tr.marker.color = color
+        # Spread bands need alpha in fillcolor; tr.opacity is ignored for
+        # fills or washes out the mean line when fill+line share a trace.
+        fill = getattr(tr, "fill", None)
+        if fill and fill != "none":
+            tr.fillcolor = _hex_to_rgba(color, 0.28)
+    except Exception:  # noqa: BLE001 - per-trace color is best-effort
+        pass
+
+
+def _apply_colorway(
+    fig, color_scheme: str, *, cell_groups: dict[str, int] | None = None
+) -> None:
+    """Colour legend series: by group when the groups are known, else per series.
+
+    With ``cell_groups`` (#181) every trace that resolves to a group — by name
+    or ``legendgroup`` — takes that group's colour, whichever way legend muting
+    is set: the scheme colour at ``group - 1`` (so ``safe`` matches the sidebar
+    swatches) or, for the ``cellpy`` scheme, the colour cellpy already gave the
+    group. Members of a multi-cell group become shades of that colour so they
+    stay distinguishable. Traces outside any group cycle the scheme in order
+    of appearance, as before; without a scheme they are left to cellpy.
+    """
     colors = COLOR_SCHEMES.get(color_scheme)
-    if not colors:
+    if not colors and not cell_groups:
         return
-    series_key: dict[str, int] = {}
+
+    def series_of(tr) -> str:
+        # A trace named after a cell is that cell's series even when legend
+        # muting puts the whole group on one legendgroup.
+        name = getattr(tr, "name", None)
+        if cell_groups and name is not None and str(name) in cell_groups:
+            return str(name)
+        return str(getattr(tr, "legendgroup", None) or name or id(tr))
+
+    def group_of(tr) -> int | None:
+        if not cell_groups:
+            return None
+        for attr in ("name", "legendgroup"):
+            value = getattr(tr, attr, None)
+            if value is not None and str(value) in cell_groups:
+                return cell_groups[str(value)]
+        return None
+
+    # group → series key → traces, all in order of appearance
+    grouped: dict[int, dict[str, list]] = {}
+    loose: list[tuple[str, object]] = []
     for tr in fig.data:
-        key = getattr(tr, "legendgroup", None) or getattr(tr, "name", None) or id(tr)
-        key = str(key)
-        if key not in series_key:
-            series_key[key] = len(series_key)
-        color = colors[series_key[key] % len(colors)]
-        try:
-            if getattr(tr, "line", None) is not None:
-                tr.line.color = color
-            if getattr(tr, "marker", None) is not None:
-                tr.marker.color = color
-            # Spread bands need alpha in fillcolor; tr.opacity is ignored for
-            # fills or washes out the mean line when fill+line share a trace.
-            fill = getattr(tr, "fill", None)
-            if fill and fill != "none":
-                tr.fillcolor = _hex_to_rgba(color, 0.28)
-        except Exception:  # noqa: BLE001 - per-trace color is best-effort
-            continue
+        g = group_of(tr)
+        if g is None:
+            loose.append((series_of(tr), tr))
+        else:
+            grouped.setdefault(g, {}).setdefault(series_of(tr), []).append(tr)
+
+    for g, members in grouped.items():
+        if colors:
+            base = colors[(g - 1) % len(colors)]
+        else:
+            base = next((c for traces in members.values() for tr in traces if (c := _trace_color(tr))), None)
+            if base is None:
+                continue
+        for shade, traces in zip(_shade_series(base, len(members)), members.values(), strict=True):
+            for tr in traces:
+                _paint(tr, shade)
+
+    if not colors:
+        return
+    series_index: dict[str, int] = {}
+    for key, tr in loose:
+        if key not in series_index:
+            series_index[key] = len(series_index)
+        _paint(tr, colors[series_index[key] % len(colors)])
 
 
 def _restyle(
@@ -1397,6 +1520,7 @@ def _restyle(
     *,
     figure_theme: str = "light",
     color_scheme: str = "cellpy",
+    cell_groups: dict[str, int] | None = None,
 ) -> None:
     """Post-plot polish: legend truncation, colorway, margins, soft axes.
 
@@ -1404,9 +1528,11 @@ def _restyle(
     ``layout_updates`` / ``height_per_panel`` (#801) in :func:`_inject_app_chrome`.
     This pass keeps app-owned legend/colorway behaviour and axis grid styling.
     """
-    # Name truncation must not share fate with best-effort cosmetics.
+    # Colour first, while trace names are still the full batch keys the
+    # group lookup needs (#181); truncation must not share fate with the
+    # best-effort cosmetics below.
+    _apply_colorway(fig, color_scheme, cell_groups=cell_groups)
     longest = _shorten_legend(fig)
-    _apply_colorway(fig, color_scheme)
     tokens = _THEME_TOKENS.get(figure_theme, _THEME_TOKENS["light"])
     try:
         strip_pad = _FACET_STRIP_RIGHT_PAD if _has_right_facet_strips(fig) else 0
diff --git a/src/cellpy_simple_gui/core/plotting.py b/src/cellpy_simple_gui/core/plotting.py
index 17da76d..3a818aa 100644
--- a/src/cellpy_simple_gui/core/plotting.py
+++ b/src/cellpy_simple_gui/core/plotting.py
@@ -68,6 +68,8 @@ def summary_figure(records: list[CellRecord], spec: SummaryPlotSpec) -> str:
         group_legend_muting=spec.group_legend_muting,
         # Named groups caption their cells in the legend (#187).
         group_titles=collect.group_titles(records),
+        # One colour per group, shaded per cell, whatever legend muting does (#181).
+        cell_groups=collect.cell_groups(records),
         figure_theme=spec.figure_theme,
         color_scheme=spec.color_scheme,
         # Unit-bearing titles; cellpy defaults are pretty but unit-less (§18 / #38).
@@ -181,6 +183,9 @@ def cycles_figure(records: list[CellRecord], spec: CyclesPlotSpec) -> str:
         family_kind=_CURVE_FAMILIES.get(spec.curve_kind, "cycles"),
         group_legend_muting=spec.group_legend_muting,
         group_titles=collect.group_titles(records),
+        # per_cell facets colour by cycle and film is a heatmap; only the
+        # per-cycle layout has one series per cell to colour by group (#181).
+        cell_groups=collect.cell_groups(records) if spec.layout == "per_cycle" else None,
         figure_theme=spec.figure_theme,
         color_scheme=spec.color_scheme,
         x_range=spec.x_range,
diff --git a/tests/test_core.py b/tests/test_core.py
index 3aec53f..5d372d7 100644
--- a/tests/test_core.py
+++ b/tests/test_core.py
@@ -1317,6 +1317,149 @@ def test_group_names_caption_ungrouped_legend(loaded_library):
     assert titles == {"Anodes"}
 
 
+# --------------------------------------------------------------------------- #
+# #181 — colour by group, shade by member, whatever legend muting does
+# --------------------------------------------------------------------------- #
+
+
+def _hue(color: str) -> float:
+    """Hue in [0, 1)."""
+    import colorsys
+
+    rgb = collect._parse_color(color)
+    assert rgb is not None, color
+    return colorsys.rgb_to_hls(*(v / 255 for v in rgb))[0]
+
+
+def _same_hue(a: str, b: str, tol: float = 0.03) -> bool:
+    """Hue equality with wraparound and slack for 8-bit hex rounding of dark/light shades."""
+    d = abs(_hue(a) - _hue(b))
+    return min(d, 1 - d) < tol
+
+
+def _line_colors(fig: dict) -> dict[str, str]:
+    """Trace name → line colour (first trace per name)."""
+    out: dict[str, str] = {}
+    for tr in fig["data"]:
+        color = (tr.get("line") or {}).get("color")
+        if tr.get("name") and color and tr["name"] not in out:
+            out[tr["name"]] = color
+    return out
+
+
+def _three_cells_two_groups(loaded_library):
+    """cellA1 + cellA2 in group 1, cellB in group 2."""
+    from cellpy_simple_gui.core import cellpy_adapter
+
+    lib = loaded_library
+    a = lib.all()[0]
+    b = lib.add_cell(cellpy_adapter.load_example("cellpy"), source="example:cellpy2")
+    c = lib.add_cell(cellpy_adapter.load_example("rate"), source="example:rate")
+    lib.update(a.id, group=1, label="cellA1")
+    lib.update(b.id, group=1, label="cellA2")
+    lib.update(c.id, group=2, label="cellB")
+    return lib
+
+
+def test_cell_groups_map(loaded_library):
+    lib = _three_cells_two_groups(loaded_library)
+    lib.set_group_label(2, "Cathodes")
+    assert collect.cell_groups(lib.selected()) == {
+        "cellA1": 1, "cellA2": 1, "group 1": 1, "cellB": 2, "Cathodes": 2,
+    }
+
+
+def test_shade_series():
+    assert collect._shade_series("#4C78A8", 1) == ["#4C78A8"]
+    shades = collect._shade_series("#4C78A8", 3)
+    assert len(shades) == 3 and len(set(shades)) == 3
+    assert shades[1] == "#4c78a8"  # the middle member keeps the base
+    assert all(_same_hue(s, shades[0]) for s in shades)  # same hue throughout
+    # rgb() input is understood; garbage is passed through untouched
+    assert len(set(collect._shade_series("rgb(76, 120, 168)", 2))) == 2
+    assert collect._shade_series("not-a-colour", 2) == ["not-a-colour"] * 2
+
+
+@pytest.mark.parametrize("muting", [True, False])
+@pytest.mark.parametrize("scheme", ["safe", "muted", "cellpy"])
+def test_summary_colours_follow_groups_regardless_of_muting(loaded_library, muting, scheme):
+    """Cells of one group share a hue; members are distinct shades; groups differ (#181)."""
+    lib = _three_cells_two_groups(loaded_library)
+    fig = json.loads(
+        plotting.summary_figure(
+            lib.selected(),
+            SummaryPlotSpec(
+                plot_type="charge_capacity", group_legend_muting=muting, color_scheme=scheme
+            ),
+        )
+    )
+    colors = _line_colors(fig)
+    assert set(colors) == {"cellA1", "cellA2", "cellB"}
+    assert colors["cellA1"] != colors["cellA2"]
+    assert _same_hue(colors["cellA1"], colors["cellA2"])
+    assert not _same_hue(colors["cellB"], colors["cellA1"])
+    if scheme != "cellpy":
+        palette = collect.COLOR_SCHEMES[scheme]
+        # The singleton group is painted exactly its swatch colour (group 2 → index 1).
+        assert colors["cellB"] == palette[1]
+        assert _same_hue(colors["cellA1"], palette[0])
+
+
+def test_summary_colours_identical_for_both_muting_modes(loaded_library):
+    lib = _three_cells_two_groups(loaded_library)
+    figs = [
+        json.loads(
+            plotting.summary_figure(
+                lib.selected(),
+                SummaryPlotSpec(
+                    plot_type="charge_capacity", group_legend_muting=muting, color_scheme="safe"
+                ),
+            )
+        )
+        for muting in (True, False)
+    ]
+    assert _line_colors(figs[0]) == _line_colors(figs[1])
+
+
+def test_cycles_pane_colours_follow_groups(loaded_library):
+    lib = _three_cells_two_groups(loaded_library)
+    fig = json.loads(
+        plotting.cycles_figure(
+            lib.selected(),
+            CyclesPlotSpec(cycles=[1], group_legend_muting=False, color_scheme="safe"),
+        )
+    )
+    colors = _line_colors(fig)
+    assert _same_hue(colors["cellA1"], colors["cellA2"])
+    assert not _same_hue(colors["cellA1"], colors["cellB"])
+    assert colors["cellA1"] != colors["cellA2"]
+
+    # per_cell facets are coloured by cycle — untouched by the group pass.
+    fig = json.loads(
+        plotting.cycles_figure(
+            lib.selected(),
+            CyclesPlotSpec(cycles=[1, 2], layout="per_cell", color_scheme="safe"),
+        )
+    )
+    by_cycle = _line_colors(fig)
+    assert set(by_cycle) == {"1", "2"}
+    assert by_cycle["1"] != by_cycle["2"]
+
+
+def test_group_average_colours_match_swatches(loaded_library):
+    lib = _three_cells_two_groups(loaded_library)
+    fig = json.loads(
+        plotting.summary_figure(
+            lib.selected(),
+            SummaryPlotSpec(plot_type="charge_capacity", group_average=True, color_scheme="safe"),
+        )
+    )
+    colors = _line_colors(fig)
+    palette = collect.COLOR_SCHEMES["safe"]
+    assert colors["group 1"] == palette[0]
+    assert colors["group 2"] == palette[1]
+
+
 def test_summary_panels_for_capacity_ce():
     panels = collect.summary_panels_for("capacity_ce", "gravimetric")
     ids = [p["id"] for p in panels]