Historical Rules · 18 February 2022
Rule 202.2a
Official source text from the 18 February 2022 Rules release
The five colors are white, blue, black, red, and green. The white mana symbol is represented by {W}, blue by {U}, black by {B}, red by {R}, and green by {G}. Example: An object with a mana cost of {2}{W} is white, an object with a mana cost of {2} is colorless, and one with a mana cost of {2}{W}{B} is both white and black.