The Gel Filter Kit is a plastic ring adapter that allows the use of 6 inch square or circular gel filters with any five inch reflector.
The adapter allows you to sandwich in between it's disks, one or more color, diffuser, or neutral density filters to modify the light coming straight out of the reflectors.
The kit includes three common color temperature shifts to make the flash look more like indoor lighting color temperatures; one green one for florescent, one yellow one for incandescent and one darker yellow for halide lamps like at a sports complex.