This doesn't look like normal sun fade. Usually UV damage is fairly consistent, and the lighter colored areas look like that kind of fading. The splotchy patterned areas look like something else. To me it looks like you have some type of bacteria damage. If your gel coat has been worn out, the UV damage may have created a little pitting, giving this stuff room and time to grow. If the glass cloth is not damaged, I would think you could sand through the this, re-glass and gel coat.

Just my two cents.

Eric M.