105.2

An object can be one or more of the five colors, or it can be no color at all. An object is the color or colors of the mana symbols in its mana cost, regardless of the color of its frame.

Sol'kanar the Swamp King. Regardless it has Gold frame, its colors are blue, black, and red.

An object's color or colors may also be defined by a color indicator

Nicol Bolas, the Arisen. Although His planeswalker side hasn't mana cost, his colors are blue, black, and red because his color indicator discribes so.

or a characteristic-defining ability. See rule 202.2.

Eldrazi Obligator. It's devoid ability makes it colorless.