_colorSet
_colorSet defines a componante of a Color object.
Prototype : fun [ObjColor I I] ObjColor
- ObjColor : a Color objec.
- I : the value, between 0 and 65535.
- I : the componante : RED, GREEN, BLUE or ALPHA.
- Return : ObjColor : the same Color object or nil if an error occurs (typically a bad object or a bad componante)