I don't actually think your pickups are turning yellow at all. I only had a 7VWH for about a year, but one of my humbuckers and the two knobs were CLEARLY more cream colored than the other two pickups. I mentioned it here, and several other 7VWH owners took good long looks at their guitars and saw the exact same thing; some pickups and knobs were pure white and some were cream, and some guys like me had a mixture of parts. Mine was a '98, btw. I spoke to a few and almost had a trade for a set of pickups to at least get two of our guitars matched color wise (either all white or all vaguely cream colored) but it didn't end up panning out.
Some of the pickups and knobs just aren't perfect white, and if you don't really hold up the guitar and stare at the pickups, you might not notice it. If all of your pickups and knobs are the same shade, I think your only option is to replace them all. If you have a mix, maybe someone here would consider swapping a neck Evo or whatever for like if they're also mismatched.
jim