Is there such thing as a perfect hue angle for Cyan and Magenta, in Lch?
There is no such thing as a perfect hue angle for cyan and magenta (or yellow for that matter) in CIELAB LCh or any other color space. The optimal hues for cyan, magenta, and yellow would depend on the application and the technology. Take yellow as an example. Perceptually unique yellow (a yellow with no perception of red or green in it) is at a hue angle of just about 90 degs. in CIELAB. So that is one definition of an optimal yellow. However, in a color reproduction system the best yellow to optimize the volume and nature of the color gamut might not be perceived as unique yellow. For example, in photographic systems the yellow primary tends to be a bit to the red side (lower hue angle).
