It is oxidation, almost all the dark gray caps are doing this from keystone, talk to your dealer, they are correcting the problem (lack of uv protection in gel coat, it is gel coat and not paint) you can polish it out, but it will return very quickly. I repainted mine, a lighter shade of gray (platinum). Made it two tone. If you decide to repaint, I would recommend Marine top coat, designed for high UV and tough.
