Color doesn't matter. No Un-Sets. In case of a tie, one card tied for highest number suffices. I need such a card as a test case for a computer program involving MtG cards.
Draco has the largest generic mana number, at 16. (Observed using the same query.)
If you include unsets (I know you didn't want that, but for completeness, and because I love them) Big Furry Monster from Unglued has 15. And Gleemax has generic mana requirement of 1,000,000.