i dont if this happens with you but when im feeding my oscars they will jump and sometime hit the lids and take a little chunk off them, is it normal that whilst heeling it will go black a bit on a tiger oscar

the wounds will heal real quickly, with pristine waterconditions, but the pigment may change indeed on the scars.
On my red the scars stay more white than his original pigment colour.
My oscars hurt their heads and backs on several occasions and indeed it happens often when they're hungry and greedy.

This is one of the thing oscars sometimes do- hungry buggers!!!

Cant you lift the lid when feeding them- but be careful they dont jump out!!!!