Dark spots on GCC wings

Hi, I'm wondering if anyone has some information they'd like to share about spots on their birds wings. I have two GCC's and one has dark spots on her wings that are close to her shoulders. I've researched it and people talk about bronzing, nutritional issues, etc. So I'd like to hear from someone about it. My birds get a good variety of things to eat, but they could eat less seeds. Thanks for any information.

Here's a picture of bronzing vs. stress bars.
Stress bars (mild in the photo) can be caused by nutritional needs not being met as seen here in my black cap conure. Stress bars can also be caused by other forms of stress.

Bronzing (mild in the photo) is a general wearing out of the colored layer of the feathers. This is common in babies as they are very active. Poor nutrition at the time the feathers were formed can contribute to the problem. Good nutrition produces stronger featheres. Oils from your hands is speculated to contribute to bronzing. Bronzing is usually not a big concern unless it is extensive.

Nutrition-wise I would advise you to check out the nutrition forum. You didn't specify what you feed, but it's very hard to satisfy your birds nutritional needs on a majority seed diet. Generally you will find people advocating a fresh+pellet+minimal seed approach.