The use of 'pigments' or 'pastels' to simulate mud and sand on tanks is seen more and more on models. (the difference between pigments and pastels is that the later is more secured to the model after application) Companies suchs as MiG and CMK produce a variaty of pigments with colors like 'european mud', 'light sand' etc. We already used pastels to simulate soot. The fact that these pastels are very matt when they dry and can be applied in thin layers also make these pigments ideal to simulate sand.
But what if you can't purchase the specific pigments or pastelscolors you need? In that case you have to mix to get the right color. We take a look at how we make a light tinted type of sand seen a lot in European training grounds. Vehicles driving around on these terrains look like this quite fast:
I usually looked at the color of the ground, mixed pastels to get that color, applied it on the model and found out it looked too dark. The reason for this is that the layer of dust on real vehicels is very thin which makes the sand look lighter. The secret of producing this with pastels is by adding a lot of white. Usually 1/3 up to 1/2 of the mixture should be white pastel. The results look like this with a mixture of about 3/8 white, 1/4 yellow and 3/8 oker colored pastels:
Remember, the pastels are applied with water and can be reworked as long they are wet or moist. Once dry they form a layer weel fixed to the model surface. Reapplying water does dissolve this layer however. So you can always get rid of the pastels applied.