As it is, I'm leery about increasing the number of colored cards in Affinity because the deck's mana is pretty bad (12 of your slots in a build have to be artifact lands, leaving you 4-5 lands to reflect the color composition of your deck).
I may be wrong, but I believe Springleaf Drum made Affinity mana alot more stable. And it's not like the deck won't run Vial. I am still not convinced Slasher is good enough, though.