Hi I'm having a light brown stain show up on some shirts kind of looks like they had rusty water on them. They don't have them from the box or after I run them through the belt dryer until they cool then there a kind of very light rusty brownish stain that shows up and there is no one place or pattern to it and it only does this on ash grey shirts any other color including white never happens I showed it to a friend of mine who runs a dry cleaner and he though it was from heat but I run all my shirts on the same settings and have seen no others with stains like these and it doesn't happen on any other color. I also cleaned the belt just to make sure nothing was on it but it still happens. I included a picture but it hard to see it kind of like very week coffee color but the customer can see it and I can see it and I don't like it so if any one can help I'd really appreciate it. Thanks

Looks like scorching:

http://www.catspitproductionsllc.com/scorchout.html

That is due to excessive heat in the oven on lighter or white garments. The cotton singes and yellows or browns.

Thinner or poor quality cotton may also scorch easier than other heavier cottons or higher quality brand names garments.

Thank you.