TL;DR
New "RGB" signal works as normal color signal, but when used in device with "Use Color" checkbox (e.g. lamp) device will use it value (with clamp [0, 0xFFFFFF]) to set custom rbg color.What ?
Add new kind of color signal which can be used as RGB color value for specific devices (with "Use Color" option).As I see it, this change don't break any existing logic.
You can set this value directly (in hex, or new smart number format) or use combinators.
Example how to convert individual Red Blue Green signals into RGB with combinators:
constant -> (BLUE, RED, GREEN)
arifmetic (* and 255) -> (BLUE', RED', GREEN')
arifmetic (GREEN' << 8) -> GREEN''
arifmetic (RED' << 16) -> RED''
arifmetic (GREEN'' + RED'') -> YELLOW
arifmetic (YELLOW + BLUE') -> RGB
Same way HSV signal can be added, for those who prefer that color model.