What does the foam look like when you grind into it? Is it melted? Is the rippled surface still rigid or is it clearly delaminated and soft? Are we looking at the top or the bottom of the hull?

That looks like a PVC foam and I do have experience melting it (heat lamp too close on a warmish day)...but it took a LOT of heat (couldn't touch it with my hand). Clearly, I couldn't say "without a doubt", but I'm doubtful that the color of the boat had a direct effect on that problem...I've seen black catamarans before with standard construction and they survive. Based on limited exposure to the problem, and while I wouldn't completely rule out some sort of thermal reaction, my first guess that there might be some sort of chemical thing happening, enhanced perhaps with the heat, to distort the foam there considering all the things that have taken place to the boat recently.