Ah...good old Rainbow Energy, welcome back to the format friend.
For those unenlightened, Rainbow Energy acts as any type of Energy, all for just putting 1 damage counter on the Pokemon it's being attached to. It is infinitely more flexible than, say, Multi, because you can attach as many as you like to a Pokemon, and they won't turn into :colorless.
Modified - 8/10 (Some decks can make great use of this, especially if they run different Energy needs)
Limited - 10/10 (Acts as any energy, and odds are you're using 2+ different Energy)
Unlimited - 7/10 (Not as powerful as DRE, but still great)