You don’t have to find all three cards. You can find two, one, or (if you really want) none.

You can find multicolored cards with Lotuslight Dancers’s last ability. For example, the black card you find could be any number of colors as long as black is one of them. Whatever colors it is won’t impact what other cards you can find. For example, you may find a card that’s black, green, and blue as the black card and still find a green card and a blue card.