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.
Legalities
Not Legal
Alchemy
Brawl
Explorer
Future
Gladiator
Historic
Modern
Oldschool
Pauper
Paupercommander
Penny
Pioneer
Standard
Standardbrawl
Timeless
Legal
Commander
Duel
Legacy
Oathbreaker
Predh
Premodern
Vintage
Rulings
2016-08-23
Any colorless mana that's produced isn't affected.