I found some stuff at West Marine or BoatUS (or somewhere) that was called something like cellulose powder. It was a very fine powder and very white. Epifanes made it as I recall. I used it as a thickener along with sanding left-overs (when I got low and couldn't find the MAS wood filler I had been using) to customize the color of my fillets and the hide the boo-boos in my Ches16lt (which I'll post pics of if I can figure out how). I was freelancing and hadn't checked the board (as I usually do), so if anyone thinks this was a bad idea, please say so before I sink into Narragansett Bay. Otherwise, the stuff seemed to work great.