Interesting. My female(the dark one) looked like your lighter male when she was about 7". now, 11 months later and 4" gained, she has turned to a darker colour. Bare bottom, and no background to influence colour either.
My male is also starting to take small pieces of flesh from the females disc, but they are very tiny amounts. and nothing too crazy like the pics you have. My female is only 2 inches wider, but much thicker, so i think she is able to fend off any big attacks the male will attempt.
Since my rays are of comparable size to yours when they started to breed, i think i can assume this is more of a matting thing rather than aggression.
I'll follow your threads and see what becomes of your male/hybrid female.
what cross is the hybrid anyway?