Support 3 channels as color

[emoon]

Something that would be cool would be if you could "combine" 3 channels for color selection. My thinking is to have something similar to the FFT view but for the active 3 channel colors. It should be possible then to select a color that sets the value for all channels at a time (from a color picker)

Reasoning is that it's very often that one wants to change colors from Rocket and while this is doable with 3 values having a color picker would be much more intuitive.

I'm note exactly sure how this would work in practice though.