Cumulative upkeep {1}{U}{U} If tapped for mana, Plains produce {R}, Swamps produce {G}, Mountains produce {W}, and Forests produce {B} instead of any other type.
"Nothing is as it seems." —Gerda Äagesdotter, Archmage of the Unseen
2004-10-04
If a player uses a text-changing effect to make a land type be listed as producing two different colors, the player tapping the land for mana can choose to produce mana of either color. But if it produces more than one mana, all mana is of the same color.
2013-04-15
If a land has more than one basic land type, the player tapping the land for mana can choose to produce mana of either color. But if it produces more than one mana, all mana is of the same color.