Why is my green shirt turning yellow?

OK so I bought several new shirts a month or so ago and they were (IMO) quite nice items I got rather cheaply from sales at Banana Republic and Express. However, the light green one is turning yellow and the darker greens are turning orange. Specifically, they’ll go through the laundry and come out with ever-increasing numbers of splotches on them. I’ve talked to one of the managers at Express and he suggested that it could be contact with the detergent, but after taking his suggestion of filling the washer then adding the detergent… my light green shirt is now mostly yellow.

I’ve also heard about the sweat stain possibility from the Internet, but I have not sweated significantly in any of the shirts. Plus they don’t look like any dried sweatstains I’ve ever seen.

What’s the Straight Dope here? Any suggestions?

You don’t use a detergent with bleach in it (even color-safe) do you? If adding the detergent last has had the effect that the entire shirt is beginning to evenly fade, as opposed to just splotches, it sounds like the detergent is most likely the culprit somehow.