The stripes on angelfish do fade away and come back on - I see this on my angels all the time. It's not stress, so don't worry

I see the fading away and coming back on of the stripes usually during lighting conditions changes; i.e., when I turn their tank lights on or off. Don't quite know why this happens, but it's kind of interesting to see the stripes fade away
Believe me, it's that "they're pigs" lol

No matter how much I feed my angels, they're literally ALWAYS hungry! So it's not that you don't feed enough, they're just like that - especially if the angels are still growing. Just make sure that you've fed them enough (say, 3 times a day - no more then they can eat in a few minutes), and after that don't worry if they're still asking for food. My adult angels don't want to eat as much as the young ones do. Once they've grown, their appetites will decrease somewhat.