[Breaking] color: Convert hue [0,359] -> [0,1]
imgui [uses 0-1 for everything internally](
https://github.com/ocornut/imgui/blob/master/imgui.cpp#L2045).
[Both Unity](https://docs.unity3d.com/ScriptReference/Color.RGBToHSV.html)
[and Godot](https://docs.godotengine.org/en/stable/classes/class_color.html#class-color-property-h)
use H, S, and V in the range 0.0 to 1.0
Since we're switching colours out of 0,255 we should also switch hue out
of 0,359. Now all of our r,g,b,a,h,s,v values are all in 0,1.
7d99a08134