A dispensing assembly for dispensing a mixture of fluids is provided. In some embodiments, the dispensing assembly includes a first valve for selectively permitting fluid flow to a mixing chamber in which a second fluid is introduced, wherein the valve is actuated between open and closed positions responsive to fluid pressure downstream of the mixing chamber. In such embodiments, the fluid pressure downstream of the mixing chamber can change based upon whether fluid is dispensed from a spray gun, wand, nozzle, or other dispensing head of the dispensing assembly.