I am noticing some feathers that have pigment loss or a shading effect to them where the color is not consistent.

Blue feathers that have an area of yellow in them and red feathers where an area is a little lighter or a little darker.

I know medications can affect feather color but I would like to know what else can cause this effect?

SUN. There is a funny antidote, don't remember where I read it.... but it discussed breeders of scarlets thinking there were orange scarlets, and red scarlets..... turns out, one group spent more time in the sun and the assumption is they faded; sort of like how brown hair can lighten up to blondish in the summer on a human who spends more time outdoors.

Also, feathers are not just the color they appear to be. This is an interesting article... Birder's World - Where feather colors come from: Why cardinals are red and grackles are shiny - Julie Feinstein I notice this most on macaw blue feathers..... flip them over and you will see yellow!

No, sun by itself could not possibly discolor feathers. We are not talking about cloth, leather or anything that was treated with dyes or which pigments might deteriorate from UV exposure, we are talking about feathers, they are meant to be exposed to sunlight.

The usual reasons are medicines, over or undersupplementation of vitamins, dietary issues, fungal growth or some kind of residue on the feather itself (like oil or something acidic).

Bea... there are pigments in the feathers... why could they not discolor? Natural or added, it seems to me they could both discolor. Back to my argument about hair.... If naturally occuring pigments didn't change, then my, my husbands, and pretty much every other person I know that spends time in the california sun would always have the same color hair all year around; It's a well known fact that it isn't.

Agree with you Dana, my birds get a bit faded like they need a wash, after molting they look like newly washed laundry, colors a bit brighter. Since most are fairly old they not getting brighter adult colors, they already have adult coloring. The suns opthalmic rings also get suntanned. My hair get red highlights in summer also. I cannot comment on exposure to uv light since I don't use any sort of lighting. I am only referring to the effects of the African sunshine. My inside birds which have limited sunshine don't have the color change that I see in the outdoor birds.

Angie - Exactly!

Just a few articles that mention sun fading in birds...

San Diego Zoo's Animal Bytes: Emu

Preparing Poultry for Show

Large Fowl-info

The Feather Conservation Survey. Introduction to Conservation Issues for the Feather Creations Seminar

Brown Base Colors

http://www.senrm.sa.gov.au/Portals/8...Life%20TRP.pdf

Birds, Eggs, And Ducks - QA

I know of something that can affect color but you probably wouldn't even want to think of it. PBFD. Lorries have quite dramatic discoloration of feathers, eventually turning very mottled, like chicks just out of the nest.
Blues turning Yellow is the first thing that happens.

Yes, of course that feathers fade. One only has to look at a new feather and compare it to the molted one it replaced to see the difference. But they would fade evenly all over the body and the discoloration would simply be a lighter shade of the same color, there would not be spots of completely different colors like described. Exposure to sun would not do that.

Yup I agree. Birds out there in the wild are exposed to all the elements.
Sun would not be a major factor in this. Wild birds are used to the sun.
Has to be something else.

Color changes or fading can also indicate liver issues. In greys it can linked to lysine deficiencies. Or it could be an over due molt. Eve changes colors all year long, while Eve is a vasa, he is still a parrot. His colors change according to hormone levels and time of the year. Right before and during a moult he is a pale light grey color, but the rest of the year is is a bluish grey, and glossy black during breeding season. But the light grey starts in patches, whichever feathers turn light first are the first ones to moult out. So it could be the same thing for your bird. Now macaws are interesting as they have been mentioned in vasa articles with respects to color change and the sun. But that reference is linked to skin color change. Wild Han's macaws that develop feather loss, either from brood patches, or mate aggression, also develop bright yellow skin on the areas exposed directly to the sun. Bare skin changing color to bright yellow is also seen in some larger macaws s well. So who's knows it very well could be the sun fading the feathers, however I would tend to try to make that assessment by process of elimination, just to make sure everything like the diet or liver was in fact fine.