Split card

Split cards are Magic cards with two card faces. A split card is literally "split" into two seperate cards each with its own card name, art, mana cost, text etc. In any zone except the stack, a split card has two sets of characteristics; while it's on the stack, it only has the characteristics of the half being played.

They were introduced in the Invasion block, where each side was from a different color. In Dissension they were seen again, and each half was a multicolored card from a different guild; finally Planar Chaos introduced the first split cars where both sides were the same color (all split cards in PC were red).

Theory

Any split card with two differently colored costs may make it easier to add into a deck striving towards Color balance.