All {W} of all mana costs and abilities is swapped with {U}. The same is true for {U} with {B}, {B} with {R}, {R} with {G}, and {G} with {W}. This ability does not effect basic lands. (This does not change the colors of spells.)

All basic plains become basic islands. Same for basic islands and basic swamps, basic swamps and basic mountains, basic mountains and basic forests, and basic forests with basic plains.