Feasibility study for the use of Cython for color editing RGB images.
Turn all color vectors towards a chosen color vector by a chosen fraction of the original angle.
Turn all color vectors away from the grey direction (angle = - <factor> * (<constant> - <original angle>)).
Scale color components independently.
Turn all color vectors araound a chosen axis by a chosen angle. The axis and angle can be optionally determined by choosing a specific color and the corresponding desired target color.