I've never personally kept mantelas so I can't say anything for certain about the coloration. I do know that they can be fragile when jumping around and into things. My tinc pair jumped around quite a bit when I first put them into their tank. They ended up with some nose rub sores that healed over quickly. No scarring was left after a week or so.
Hopefully someone with some more mantela experience can chime in to help you figure out what it may be.