I really like the concept. And I really hate the symbol. The colored backgrounds corresponding to the colors of mana look like crap. And what if someone is colorblind or the lighting is poor? I suppose you could always look at the text box to see the thing saying "X can be paid with either..." but still, it wouldn't have been that hard to stylize them differently for each color (and so that they look less like crap). Still, I really do like everything else about it besides that...