A method and system are provided for dispensing a colored polymerizing composition. Two reactive components and one color component are pumped from respective containers at a metered volume. The color component, which is preferably a low-viscosity automotive paint is injected into either the first or second stream of reactive component at a point immediately prior to mixing all components in a dispensing device for dispensing the resulting colored fluid mixture onto a surface to be coated. The mixture may be dispensed by pouring or spraying onto the surface. The method and system are particularly useful for mixing and dispensing colored polyurethane or polyurea coatings, such as for spray-on truck bed liners.