Use ColorMixin

[p3lim]

Consider using ColorMixin for everything in the oUF.colors namespace.
This would let us use the handy methods from the mixin, including :GetRGB() instead of unpacking the color object like we do today. Blizzard is using this for a decent amount of their own color objects (e.g. RAID_CLASS_COLORS), and so should we.

This is obviously not possible to make backwards compatible, so I'm putting it up for discussion before next major.