Setup color constants for handy values

[davesmith00000]

We have something similar in Indigo:

https://github.com/PurpleKingdomGames/indigo/blob/main/indigo/indigo/src/main/scala/indigo/shared/datatypes/RGBA.scala#L56

But where above we define them as Hex values they'd need to be UV vec4s (unless we do #94 first), and we'd need to make sure they'll inline correctly.