I have the small blue WM tarp I am sure you are talking about, it's a pretty good deal for a small lightweight tarp. If it's the same one it's made from thin nylon similiar to what a tent rain fly is made of, just not super light like the more expensive tarps. As for painting it...you may ruin the tarp with spray paint, with that being a very thin material that is also coated with a waterproofing film, I'm afraid the chemicals in spray paint would damage it. Krylon does make a plastic fusion paint that might work if it didn't damage the material though. One other idea that may work would be to dye it. RIT makes fabric dyes that you mix with hot water and submerge the fabric, possibly this would help to subdue your bright blue tarp.