I'm having the exact same problem on a year old nexus 10, that is a central pale yellow brown stain most visible on a white background.
It looks like a nicotine stain as if some heavy smoker had been handling the screen. Initially I thought the screen protector had yellowed so I removed it but no improvement at all.
I've got the same issue of the screen turning a kind of dirty yellow on about 75% of the screen. I bought it on first day of sale release. I think the it's been yellowing for about 2 months or so. Also have gotten a significantly shorter battery life in the last couple of months or so. Thinking of putting in a new battery. Great unit. Getting kind of kludgy though. I have to keep killing apps that start up and run on their own.
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