One of my females has white marks on her head while I had her in a trio situation, once i removed her and set her up with her own male they disappeared. My guess is that they are at least partially stress related because my misting situations did not change.
:It sounds as if your crested(s) are not shedding well enough. You may want to mist them more than what you are doing now. I would check the humidity, and make sure it is not too low. What type of enclosure do you keep you crested? How many times a day do you mist?