Sand...deserts.....

The only sand I've ever painted has been coastal sand, beaches and so on - that's not especially easy either, because sand does vary a lot in colour (especially when wet, obviously). Desert sand ... dry stuff, baked by the sun, yet fluid ..... hmm. If I were trying to paint it myself, I should employ a bit of spattering, of darker and lighter colours and lighter on darker); would introduce some complementary colour, particularly where cloud or any vertical features cast shadows; and would keep the colour and tone generally light - I know someone who, when painting in oils anyway, used Flesh Tint plus white for sand - not sure how well that really worked, but then I couldn't find any other use for Flesh Tint other than for distant figures. I think I'd go for a classic burnt sienna/raw sienna mix, yellow ochre being a touch too opaque; or Mars Yellow and Mars Red, if you have them - and as light as possible. It's conventional wisdom that the sky should always be the lightest part of the painting, but very often that doesn't work at all, particularly if you have a wide stretch of sand. On the whole, I think I'd go with brush-strokes rather than sponges or crumpled bits of this or that: study the surface, see if there are stones, rocks, bits of grass or other appropriate flora, and let these help you introduce some form into, especially, the near ground. They cast small shadows, disrupt the smooth surface, allow little touches of blue-violet shadow. And avoid the dreaded brahn...... This is how I'd approach it if I were doing it, mind - I'm not guaranteeing anything!