I'm sure some juice makers (sellers) do use coloring for their juice. Hard to explain the green, blue, or pink juices I've seen sold locally. I don't really have an issue with that, since I use only RDAs. I do think they look cuter and nicer.
I make most of the juice I vape, and all the ingredients I use have no coloring, so my juices don't have any color other than what danny mentioned above. I particularly noticed that higher-VG mixes tend to develop more amber-ish colors after steeping.