Historical Rules · 17 April 2020
Rule 202.2a
Official source text from the 17 April 2020 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.