Red has been tested here before. One of rock lee's top 8s had bonfire. You can see the discussion about it in the area of this post:
http://www.mtgthesource.com/forums/s...l=1#post761885
Punishing Fire Engine, Bonfire, Through the Breach, Sudden Shock, reb all tested well. However, it was ultimately concluded that the for UGr, options were not worth the inconsistency, and shaky mana. UG can cover those roles quite well with its current tools while keeping the redundancy and resiliency.
Mono G might have some use for a red splash, but that's a question for BoozeCube to weigh in on.
DRS black splash has always tested the best for me.