There is two ways I might go about this.. First there are products out there that are mixed with wax that have a color base in them.. In your case you would get a straight yellow.. After that I would just wax and buff about three times. Before I did that I would just try a simple wax and buff about three times.. I remember the first ski I got about two years ago... The guy sold it to me and about two weeks later I met up with him at the lake.. He could not belive it was the same ski... All I used was simple green to strip off any gunk, and then I started to apply the wax and buff... I do use a power wheel to buff but I would not recomend it, due to the fact that is a good way to scorch the gel coat if your not very carefull.