A cup liner for a cup of a spray gun includes a fluid reservoir portion that defines a reservoir and includes a divider portion dividing the reservoir into two or more compartments. Each compartment contains a fluid to be dispensed by the spray gun and keeps the fluids separated from fluids held by other compartments. In addition, a fitting for a spray gun includes two or more inlet interfaces and an outlet interface. Each inlet interface couples to a fluid source and the outlet couples to the spray gun such that the fitting provides fluid communication between each fluid source and the spray gun. This permits the spray gun to spray a mixture of the fluids.