Even after you've washed it again the problem persists. The timing is probably unfortunate as well - it annoyingly happened to my faithful Tour de France T-shirt just before the grand depart in Yorkshire in 2014.
On this occasion to try and resolve the issue I grabbed a roll of packing tape and tried to use its stickiness to get it off. Unravelling long lengths of tape and sticking them to the tshirt. It did have some effect, but the whiteness was still noticeable.
As my Tour de France T-Shirt (sadly) only gets an outing during one month of each year, I had forgotten about the problem until I retrieved it from the bottom of my T-shirt pile come next July - so had to suffer the indignity of the unsightly blemishes for another year!
Not to be caught out for next year, I'm getting ahead of the game and trying to get it fixed asap though, if you've ever googled this problem you'll see that the only real solution would seem to be soaking it in an aspirin solution. Though any significant amount of references to it actually working were sparse as the whole www seems to be just regurgitate the same urban myth.
Given a packet of dispersible aspirin costs less than 30p and the likelyhood of it damaging my clothing was low I though I'd give it a shot. It was just as I was doing my final wash in preperation for going on my recent safari holiday that I gave it a shot on a pair of black shorts which had suffered the same fate.
Put a couple of disposible aspirins in a bowl of warm water, let them disolve and give it a bit of a mix. Then all you need to do is to let soak overnight and then I put them through the wash again.
As you can see from the picture above, it did absolutely nothing, what a waste of time!