Sun conure wing feathers appear lighter, aging or illness?

[Siaarn]

My boy Sunny has had some discolouration in some of his Wong feathers, it's been a very slow gradual progression and I'm not sure it's actually getting worse or not. He's 12, so not quite a spring chicken, but I wouldn't say he's old either. He had a yeast infection early this year which cleared up with antibiotics.

I am disabled and the avian vet I took him to has moved an hour away, so I'm hoping to rule out as much as possible before I have to take him to the vet.

Photos attached are a comparison between wings, his left wing seems fine, it's just the right wing. Is it just an age thing maybe?

 

[HeatherG]

That is certainly very pretty but yes, could be related to a problem due to aging, or a liver issue.

 

[Ronnie27]

Well, it could be related to lack of vitamins, an infection or fatty liver disease.
What does Sunny eat in an average day? Does he get some exposure to sunlight? Did the vet said he had fully recovered from yeast infection? Has he taken any probiotics after his treatment ?