10 gallon is way to small for one angel let alone two. you need to either take them back to where you got them or get a new tank that is bigger than 30 gallons.
the color of one may change faster, or they might just stay the way they are.
First of all, 10 gallons is WAY to small for 1 angel, let alone 2. If only 1 eye is red it sounds to me like an injury. Have you seen any aggression between your fish? Are there any sharp objects it could have hit?
I doubt the shark attacked the angel, it's just not their style. It's hard to tell whether this is an eye injury as well though. Some Angels eye do in fact get the red through it due to the species or what have you. Would you e able to take a clear picture of the said eye? Is the fish acting and eating normally? Have you tested the parameters of the water?
and finally, I'm with jm, get those fish into a 30 or above asap...
if you keep these fish together in that tank, besides being stunted and dying an early death, you will see some MAJOR agression problems. in fact, you may be already.