Hi!
Thats normal wear and tear.
Its not stress bars , and not over preening .
Welcome to the world of non stop worrying about our feathered friends
What's your birds name? Is this a lovely Amazon? Love to see the whole bird
I would suggest adding perches of different types. And bird safe stuff to chew on. Lots of stuff you can make yourself if no bird stores near by.
A great diet that includes leafy greens and veggies, and stuff to chew up, will keep those feathers looking great. And help prevent any feather destruction behavior in the future.
Now that is a ton of information regarding your Amazon! Specific Amazons have natural black occurring on specific feathers. On a green feather, water (wet) or coming in contact with a natural oil surface with cause a feather to turn black. A feather that has a slight damage to the feather surface will reflect in black.