If white, blue etc use SEA GLOW- no sanding!
I used to have a piece of light blue hobie cat for demoing my products at boat shows. I not only demonstrated that our cleaners took of dried adhesive residue, but SEA GLOW with light scuffing (3M pad 000 very fine grade) then paper towel soaked in SEA GLOW (use like a skin lotion). This allowd SEA GLOW to penetrate pores in the old gelcoat and restore to original color.How does it work? It removes chalk from micropores that ligthen dark geclaot and darkent light gelcoat (thourhg accumlation of stains). ALso the fluorescence in the SEA GLOW "brightens" the pigment to orgianl brigtness.THa amazing thing was that you could now "feel" the step between original gelcoat and old compounded out gelcoat but could not see the color difference.On Beige hulls etc our "CRYSTAL CLEAR" (soon to be relabelled "NEUTRAL CLEAR") product is used (not need or desire for fluorescence. Go to the testimonial section of this site's chandlery to see a testimonial backing up my own experiences.WIth all due respect to the other suggestions sanding of gecloat should be avoided wherever possible and bleach is not a great idea. Why try to age good gelcoat (that had been under the sticker) rather than rejuvenate old gecloat around it?Thanks Jim Willis