Love it, your my new best friend, call me every 10 minutes. Suggestions follow.

Casting stat should probably be dependant on color involved. White and green should cast on wis, red is cha, blue is int, and black could go cha or int. It fits flavorfully, and could add an interesting angle to the class.

Boon save dcs are useful at the level you get them, but quickly become crap. Something like 10+relevant ability mod+1/2 lvl is pretty standard for most class abilities that give saves. Maybe reduce to 1/3lvl if you want them weaker.

While not so often in recent years, red has also had cold type stuff in it's color pie. Other non-burn for the red caster: Haste(representing haste of course, and first/double strike), Daze effects (target creature can't block this turn), damage increasing buffs (target creature gets +x/+0), and maybe some luck related stuff (since redc has most of the coin flipping).