_colorSetPref
_colorSetPref defines a predefined value to a Color object.
Prototype : fun [ObjColor I I] ObjColor
- ObjColor : a Color objec.
- I : a predefined color : WHITE, BLACK, RED, GREEN or BLUE.
- I : the ALPHA value, between 0 (transparent) and 65535 (opaque).
- Return : ObjColor : the same Color object or nil if an error occurs (typically a bad object or a bad predefined color)