At the beginning of each player's upkeep, that player chooses a color. Until end of turn, lands tapped for mana produce mana of the chosen color instead of any other color.
(04/10/2004)
Although the color may be altered, any restrictions on the use of the mana are not removed.
(04/10/2004)
Will not affect lands that do not produce mana.
(23/08/2016)
Any colorless mana that's produced isn't affected.
(01/10/2008)
This has the supertype world. When a world permanent enters, any world permanents that were already on the battlefield are put into their owners' graveyards. This is a state-based action called the "world rule." The new world permanent stays on the battlefield. If two world permanents enter at the same time, they're both put into their owners' graveyards.
