Because Dunkelgrau RAL 7021 presented a very stark contrast against snow, OKH decided to provide the troops with white paint to paint the equipment during the winter. The paint was water-soluble, so that it would run off the equipment when the first rain started to wash away the snow. To prevent having to re-paint stencils, tactical numbers and unit emblems, these were often left without whitewash.
Because of the large distances the whitewash had to be transported, and relatively small supplies of whitewash, several vehicles only received whitewash sparingly, if at all. Some units had to be creative, using chalk or even sheets to provide some kind of camouflage. Stacked snow on the vehicles was also used. Some of these interim solutinos were obviously better than others, also depending on the conditions. For example, where a solid white cover would blend in very well against a snow-covered field, an iregular pattern would be more suitable against a wood, where the trees would be left uncovered with snow.
Keep in mind that mid/late war vehicles were covered in Dunkelgelb with variations of RAL6003 Olivgrun and RAL 8017 Dunkelbraun/Schokoladenbraun so these should be the colors showing through.