I had some Kavon samples and it looked good but I never ordered from them. But it could have something on it. Maybe something got on it during the handling of the nylon in your shop. Unless it turns loose from the whole boat there is not much way to know for sure. But if it is only in spot(s) then I suspect some sort of contamination, but how to find out I don't know. Testing some scraps might answer it but it might not.

I have one I died with acid dye, coated with Tuff Coat and 99% of the color has faded out and no one knows why. Not a clue!