Gelcoat
No matter what you do, gelcoat does not do well when exposed to the sun. Neither do those decals. I have never seen the discoloring as it appears but it has to be from sun damage. I would be curious if you try using McGuire's gelcoat finish restorer with a good orbital buffer to see if it removes the discoloring or only brings back the shiny finish. Eventually, you will have to decide what to do with the stickers because they will not hold up to the sun exposure.
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