I've heard it can be affected by what they eat.

I've noticed very subtle yellowing also. In March, as the temperature heats up, the males seem to turn yellow almost in a week or two. My concern today is that Goldfinches outnumber all my Cardinals, Chickadees and Titmice put together and often monopolize all eight perches at the two black oil sunflower feeders which they empty rapidly. At what point are they considered a pest?

Well, if you're going to put food out that so many birds eat, I would expect anything to happen. I wouldn't consider any of them that show up as "pests"........just birds looking for food.

Maybe you should try putting different types of feeders up.....like a thistle feeder (which the goldfinches seem to prefer), and a suet feeder (which chickadees and Titmice, wrens, nuthatches, woodpeckers like). Its hard to believe that goldfinches would keep those others away. I didn't even know goldfinches liked BOSS that much.
And maybe its the type of feeder you are using with your sunflower seed. I've found that cardinals don't like those little perches........so maybe its the build of your feeders that are attracting certain birds more than others?

It's true the Cardinals have trouble staying on my perches and spend much time on the ground eating spillage. Goldfinches do indeed relish BOSS which I provide because it's cheap in large bags and popular. I have two suet feeders and get my share of woodpeckers, C. wrens, nuthatches and others. Just put off by the flocks of Goldfinches. Call me an anti- Goldfinchite if you like.

LOL. Maybe they're just having a good year! It might be different next year.

I have many goldfinches also right now in SC. They do it on occasion a few times a year and then they settle down after a while. I don't mind them though since the other birds also get their turn.

Put up a thistle feeder (nyger seed) and that should take care of them. I love my goldfinches especially in spring when they sing their sweet little tweets.

Funny how we don't like large flocks of one kind of bird at our feeders. :)

I agree. We have had around 40 finches at our feeders all winter. Then again, we often get pretty large groups of other birds at once as well. I had 14 doves a couple weeks ago and 18 cardinals this weekend in addition to the regular downies, chickadees, titmice, and nuthatches. I'm happy to report our red breasted nuthatch is back and we had a mockingbird stop by. We have more juncos this year as well. It's kinda crazy what I spend on those birds, let alone the 30 mile drive to our farm. I have to "invent" other reasons for going down, but the truth is we really go down for the birds.