I am trying to handle my chicks frequently and checking for pasty bum. But it is challenging - all 4 look the same. I read about marking the chicks on the top of their heads to differentiate the four babes. So I tried it on 2. The chicks immediately started pecking on the heads of those marked. I did not use red. I feel so stupid. Of course I tried to wash it off, no go. I then used a gentle eye make-up remover on a Q-tip and then washed with a clean wet pad and dried with a clean cloth. I pray I have not damaged these little chicks. Anything else I should do to correct this situation?