A system and method for custom coloring sealant is generally provided with one or more dispensing cartridges, containing a quantity of low viscosity sealant base solution, which in some embodiments is as fluid, or more-so, as common latex paint. One or more such dispensing cartridges are secured within a cartridge case. A coloring agent is added to the dispensing cartridge. The system may then be agitated by hand or in a mechanical agitator, such as a commercial paint shaker, until a desired color is attained. The sealant thickener may then be added and mixed by similar agitation of the system to obtain a non-sag, high viscosity sealant. Embodiments of the cartridge case are provided for use with various mechanical agitators and dispensing cartridges.