Its likely yeast or proteins, nothing to worry about. Some of the krausen will never settle and just sit on the surface until I rack the beer off of it.
Primary: Apfelwein, Raspberry Lambic, Experimental Wheat cider, IPA
Keg 1: Hefe
Keg 2: Irish Stout
Keg 3: Peach Kolsch
Keg 4: Empty
Bottled: Bourbon Vanilla Porter, Chocolate Stout