hmmm red gelcoat....never dealt with that before hmmmmmmm well on the white, fiberglass gel coat I use
a type of wash wax mix so try that, works brilliantly
Discolered I cant really help you with because in my case its never "discolored" since it is white, I use black streak remover on the vessels I wash, mildew remover and good ol wax. THat usually keeps her spiffy
I know there is a product called lacquer thinner that friends use for extreme stains and stuff so you could try some research on that
Good Luck
Matt