From the original questions I assumed (wrongly) that your new toy had faded gelcoat and good(ish) gelcoat where the striping/letters were. However, from the photos, I see that what you are dealing with is staining to white gelcoat. I don't know that sanding/buffing will help in this case. The staining may go some way INTO the gelcoat as it's a porous coating.

I know that there are bleaching products available for GRP but have never used any. Perhaps someone else on here has experience with removing staining?