I posted the name of a video on gel coat repairs for boats a year or two ago. The video shows you how to prep and colour match the gel coat colour. Gel coat does not change colour when it sets like paint
. It does change colour over the years like everything else, mostly on the surface.
You clean and prep the area. Match the gel coat colour testing it right on the finish without the accelorator. If OK you simply wipe of the gel coat, add the accellerator and finish.