Do you need to paint it? That looks a fairly good natural colour to go with!
I made a test piece a few months back to work out the colours for my sic-fi basing and to test the material and the mat's durability.
I've found that painting the mat gives it a more stable surface and traps the sand/grit in the paint. The unpainted mat shed its sand quite badly and was very harsh on the figures. Painting it also has the benefit of all the terrain and figure bases matching the playing surface, something that I'm a bit OCD about

Image below shows the test piece with the test terrain items and some figures (excuse the quality, it was taken on a mobile).