Here's my modified '88 Strat Plus which shows that the pre-yellowed "vintage white" finish gets yellower with age. Presumably this makes it "even vintager white"...
With jackplate removed to show the original finish:
Truth be told, I'm not mad keen on the yellowing. I like the effect in moderation (like CeltRocka's Squier) but I wish mine was a bit less yellow! I've experimented with rubbing the body lightly with 0000 steel wool and this seems to lighten it up a bit (presumably I'm removing the yellowed surface of the top coat?). I'm probably going to disassemble the guitar and do it a bit more thoroughly as I quite like the effect. I'm not going to start throwing screwdrivers at it or anything - just a light relic feel and a lighter shade (of pale

).