The technology of the present application provides a flex or flexible tint system for stains. In certain aspects, the system comprises a known volume of an unpigmented stain and a colorant cartridge of containing a known volume of colorant. The colorant cartridge has a movable bottom and a discharge nozzle at the top. The movable bottom is movable along the colorant cartridge to consistently deliver a known discharge volume of colorant to the known volume of unpigmented stain. The colorant and unpigmented stain are mixed to achieve a stain of the desired color consistently.