Here is a mod which clears the dirt with different parameters to obtain some kind of dirty sand looking stuff,
without modifying the original mp4 textures.

These parameters are : Luminosity levels | Color Balance | Vibrance | Selective colors.
It also changes the colorimetry of grass to match dirt's color and use different inflatables for more realistic ones.

This mod was built for dirt-heavy tracks.
Near-beach ambiance with minimal changes to keep that classic nadeo look.

ClearDirt mod > http://www.maniapark.com/ressource.php?id=3788

Screenshots :