Thank you so much for your support and for trusting us for your carry holster. We hate to hear that your shirts are experiencing underarm discoloration, and we completely understand why that would look like a dye issue.
What you are experiencing is actually a known chemical reaction, rather than a defect in the fabric dye. Many antiperspirants contain aluminum or acidic compounds. When these mix with sweat, they form a localized acid that can permanently alter or "bleach" textile dyes (especially on green or dark garments). (Another culprit is skincare products containing benzoyl peroxide, which causes identical bleach marks when the shirt is pulled on or washed)!
You've been an awesome supporter of our brand, we want to make sure you have a fresh shirt to wear out. We'd love to send you a replacement shirt on us. To help protect the next one, we recommend switching to an aluminum-free alternative and letting the deodorant dry completely before wearing the shirt.
You should get an email shortly about your replacement shirt.