Today it took me the whole day to check out this small dirty trick:
If you are using the Drupal Theme Pixture Reloaded, all changes in your style.css are not applied automatically. Like every other Drupal Theme, which supports the Colour Module, you have to klick „Save Configuration“ in your theme configuration dialog. Only after klicking it, your style.css gets read out. Otherwise your old cached css file is used.
After that i had another problem: My Theme was broken after reading the style.css out. I just had to delete the /sites/default/files/color folder and everything worked fine again.