Aparantly, by definition, a rainbow deck is 5+ colours.
Anyway...I've always heard about the infamous BH+Discord combo but I haven't seen many actual BH+Discord decks posted.
So, here's my take:
6tt 6u3 6u3 6u3 6u3 6u5 6u5 6u5 6u5 6ve 6ve 6ve 6ve 6ve 6ve 749 74a 74f 74f 74f 74f 74f 74f 7dm 7dm 7n2 7n2 7n2 80h 80h
Discords, as useful as they are, are very fragile with only 3 life.
Soloution?
SN+Quint.
Basically you wanna scramble their quanta then drain it and heal yourself with black hole.
The demon and shield work together very nicely in killing dangerous creatures.
Momentum and Explosions help your discords to break through shields.
You only really need 1 discord to do some damage so that's why I didn't go with the full 6.
Add your own suggestions.