Abstract: A cap for a spray gun for spraying a mixture of a first fluid and a second fluid. The cap includes a base removably mountable to the spray gun. The base has an aperture in fluid communication with a supply of the first fluid upon being mounted to the spray gun, the aperture configured for spraying the first fluid. A secondary port receives the second fluid to be mixed with the first fluid. A removable conduit conveys under pressure the second fluid to the secondary port, the conduit extending between a supply fitting in fluid communication with a supply of the second fluid and removably mountable thereto, and an opposed release fitting removably mountable to the secondary port, the release fitting being positioned, shaped and sized for directing the second fluid into the first fluid, thereby forming the mixture. A pressure system for the spray gun is also provided.