Rules · PlanesAdvisor

202.2 An object is the color or colors of the mana symbols in its mana cost, regardless of the color of its frame.

202.2a 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.
202.2b Objects with no colored mana symbols in their mana costs are colorless.
202.2c An object with two or more different colored mana symbols in its mana cost is each of the colors of those mana symbols. Most multicolored cards are printed with a gold frame, but this is not a requirement for a card to be multicolored.
202.2d An object with one or more hybrid mana symbols and/or Phyrexian mana symbols in its mana cost is all of the colors of those mana symbols, in addition to any other colors the object might be. (Most cards with hybrid mana symbols in their mana costs are printed in a two-tone frame. See rule 107.4e.) (refs: 107.4e)
202.2e An object may have a color indicator printed to the left of the type line. That object is each color denoted by that color indicator. (See rule 204.) (refs: 204)
202.2f Effects may change an object’s color, give a color to a colorless object, or make a colored object become colorless; see rule 105.3. (refs: 105.3)