I was afraid of this. How long did you have it before it started turning yellow and are you sure it's not like the oil from your hair plus sweat stains ? Also, where did you hear about the white Pro700MK2?
I've been to Japan a couple of weeks ago. Visited the Audio-Technica company store. It is there on display along with the white M50. It is still not in production. My Pro700 started to get yellowish about 3-4 months, it is certainly not sweat because the whole headband is like that including the ear cups. My head is not touching the upper part of the headband for sure.
Same with the white Sennheiser Adidas they turn yellowish, I even tried to bleach and buffer it with very fine sandpaper, no use. So I decided not to get anything white. Anything that is exposed to fluorescent lighting, sunlight, and oxygen turns yellow for sure, unless it is coated like those glossy Macbooks.
White electronics is simply a no-no. Glossy white will get scratched, while matted white will turn yellow.
Edited by alvincapalad - 3/6/12 at 11:32pm