Incorporation of dyes directly into the formulations has not been very successful, since many dyes adversely affect the catalysis. Coloring with either organic or inorganic pastes is the preferred method. Colored urethane foams are required in some applications. Most colored foams are produced by adding color pastes. These colorants are used for dispersion in polyols. Urethane color pastes, which are dispersions of pigments in a polyol or plasticizer. When using color pastes, compensation must be made for the hydroxyl value of the pastes by adding additional isocyanate. A complete range of colors is obtainable by blending the primary colors (red, blue, and green). Carbon black pastes are easiest to use. It is important that the color paste be compatible and stable with all components to which it is added. Generally, no other formulation variables are required when color pastes are used.