Use _luma rather than _simple simple item colors for wpcolor

Use _luma rather than _simple simple item colors for wpcolor

_simple colors seem to be used far less, and some of the colors are
quite dark, like the shotgun's "Cinnamon brown". This can make aiming
with it very difficult on some maps. _luma colors are used by more
people, are generally brighter, and better reflect the weapon's "true
color", so are the better option to use for wpcolor.