UV support

[stonegray]

Currently there appears no way to specify UV in 1.0.0. I've tried setting it as a cyan or magenta channel, but the color picker doesn't seem to let me use only that color.

This also occurs to a lesser extent with amber; there's about 30/255 leakage of other channels making the orange appear washed out.

Color is complicated and I don't have a good solution, perhaps being able to switch a scene into a mode with sliders instead of a palate might be a temporary solution? I'm not clear how blending from/to UV should even work so perhaps keeping it separate makes sense.