There are two variations of the cover of Schlagers!, shown below. In one, the mountains have a blue tone, in the other they're more gray. To be honest, I'm not sure which would be the "basic" color. Some of the singles have what is clearly a basic color that has been hand colored to make it look different. Schlagers! doesn't give me that same impression.
If you know of any other variants, please drop me a note.