Markus,
The sands of mars have a range of colours from light rusty red through to a very dark material which results in the markings you see.
But the lighter material is very fine and is blown around in the dust storms and covers over the darker material, hence the features you see change.
In addition to that many of the markings we see from earth are huge fields of sand dunes which move, slowly blown by the wind just as they do on earth.
See for example
https://apod.nasa.gov/apod/ap160720.html