Sometimes when chickens have mites they will get naked butts. Make them a dust wallow with play sand wood ashes and Diotomatous earth. They will dust bathe in the mixture and it will kill the mites. Some people add the insecticide Seven to the mixture for added killing power but I worry about the effect of it on the eggs. Enjoy your chickens.

Can you see mites? With the chickens and eggs being white, shouldn't I be able to see the mites? I haven't seen anything on the chickens or the eggs.

You can see mites if you look VERY closely, but they are tiny little suckers. Your birds might be picking each other out of boredom and/or overcrowding. If you click on my 'My Page' link there is tons of chicken info there, on both mites and keeping your girls happy, that might help you. :)

Velvet

Do your chickens get any sun time? You said they were indoor chickens. Perhaps they could use a small outdoor run to soak up some sun vitamins and a little green grass. The color of your egg yolks will improve and so will the hens over all health. It will give the hens something to do besides pick each other, which they will do when bored or over crowded.
I have a bunch of 10 week old buff orpington pullets which were stuck inside due to bad weather. They tried to pick my Easter Eggers bald. It all stopped as soon as they were moved outside where they could pick grass and bugs instead. good luck