Reality Twist — ruling 1

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.

Reality Twist — ruling 2

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.

Reality Twist : règles, fonctionnement et interactions (MTG)

Reality Twist is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

Cumulative upkeep (At the beginning of your upkeep, put an age counter on this permanent, then sacrifice it unless you pay its upkeep cost for each age counter on it.) If tapped for mana, Plains produce , Swamps produce , Mountains produce , and Forests produce instead of any other type.

How it works : Reality Twist

Original English text — Wizards of the Coast / Scryfall

#1April 15, 2013· Wizards of the Coast
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.
No other card is named in this ruling.
#2October 4, 2004· Wizards of the Coast
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.
No other card is named in this ruling.