Prismatic Wall

Prismatic (You may spend only colored mana to cast
this spell. It becomes those colors as you cast it.)
Sunburst (This enters the battlefield with a +1/+1 counter on it for each color of mana spent to cast it.)
Defender
Remove a +1/+1 counter from Prismatic Wall:
Add one mana of any color. Activate only as a
sorcery.