The white stuff sounds like extra calcium deposits it has happened to my girls once in a while maybe one girls is eating to much oyster shell I would use the lipstick or food coloring idea or take a morning and go sit in the run and watch who lays what egg I have done that. Spent a day outside with the girls while I was working in the yard checked the nest box after each hen to see who laid what have a pretty good idea who lays what color now. I have a few new hens so I need to spend the day doing this again. I think for my chart I will use a picture of the hen and a picture of the egg since my memory seems to be going.
good luck with your hen.
