Greyish Patches on White Clothes?

Question:I've recently washed a newish t-shirt (my favourite one). The first time I washed it, I did it by hand, but only because I had no money for the laundrette; it says it's machine washable. After a time in the machine, the t-shirt has been left with greyish patches all over it. Hoped washing it again would get rid of them, but while no more have appeared, the first lot haven't gone...
Any ideas what this is and how to get rid of it? I love this t-shirt and can't get another the same. :(
Thanks

Answers:
Go to Wal-Mart or K-Mart, go to the laundry section and look for "RIT"-'Color Remover'. It comes in a little box, close to the size of a pack of cigarettes(100's). It's usually with the 'RIT' dyes. It really works!! If you can't find it, just ask somebody. Most people that I know already use some of the 'RIT' products, and can tell you where to find it. Good luck!! Oh, and you may need to get two boxes, just to be on the safe side!!