Could be just absorbtion of atmospheric pollution, tannins, etc. into a porous gelcoat repair.
Try removing all the old dead wax with a strong alkaline detergent, rinse well, then bleach the staining with oxalic acid.
Oxalic can be obtained in a paint or hardware store.
If that''s the cure, be sure to ''close'' the surface by high speed power buffing and then making sure you keep a good wax on the surface to seal the surface.
Hope this helps.
I would start with wiping down with acedtone
or interlux fiberglass cleaner. My next step would be to wet sand with 600 or finer. This will tell you how deep the discoloring is. If the brown color remains your only option is to have it redone.Could this area have come in contact with fuel said from and over flow.
diesel inspection/cleanout port
It finally happened. My gunky fuel got to the engine. Anyone know what kind of ports I can install in my fiberglass fuel tanks that will not leak and hold up to the sloshing diesel? What about bedding and sealing?
We had similar brown discoloration problem with epoxy filler (WEST) repairs that I made to our deck - filling in dings and cracks. That was due to UV rays degrading the epoxy, and we ended up repainting the entire deck. Fiberglass gelcoat should not have this UV problem, so there may have been a contaminant in the gelcoat mix, or as some have mentioned above, a separate spill or stain. If the mix was contaminated, you will need to grind it down and do it over.