Adding a photo gel to your beauty dish can be an easy way to balance your strobe to ambient light color temperature (color correction), adding a creative color tint to your subject, or to add a splash of color to your background. I like to use a warming filter on my key light (which is a Paul Buff 22R dish) because it helps in achieving nice, warm skin tones on portraits.
The easiest way to gel your beauty dish is to measure the distance between the back of the dish and the diffusion reflector. Then cut a strip of gel as wide as that measurement and as long as the circumference of the reflector supports (image attached). In the case of my 22R the strip is 3 3/8 x 21″. Finally, I taped the two edges of the gel together so the gel wrap is nice and tight.
Take precautions to cool down your strobe occasionally if using a gel on your beauty dish because the combination of the modeling light and the flash will generate a lot of heat which is trapped by the gel.
For additional reading please visit a full review of my Paul C. Buff beauty dish.