[nomoreyellow123]

FYI oxyclean is quite good at this, and so far hasn't damaged any of my clothes including dress shirts. The key is to soak the collar in very concentrated oxyclean solution (~1 full scoop or more per gallon) for several hours, and then wash the shirt like normal. Yellow ring disappears. I've even gotten pen ink stains out this way, which was incredible.

[dnr]

I just used oxiclean whitening for the first time and it made a bunch of white shirts (dress shirts and undershirts) look nearly new again. Pretty impressive stuff, and cheap too. Only downside is it made the fabric feel a little stiff and rough after drying. Next time I'll try a little vinegar in the rinse.

Tip: get some rubber gloves to deal with the concentrated solution.