Kinda hard to see, but in hand it's pretty clear...
Copped two pairs of these Air Trainer SP1's (or whateverthehell they're called) at my local Nike Clearance store (one for me one for @sonsofblackmaria ) and noticed the yellow on each pair is slightly different...the one on the left is more like the Jordan IV 'Thunder' yellow (kind of darker) and the one on the right is like the Air Max 97 'Air Sprung' yellow (which is a bit lighter)...and both came from the same factory with overlapping production dates.
I painted houses for a couple of summers in my early 20's so I notice these kinds of things. I find it interesting to see that slight differences in color shades don't just happen with houses, but also within these controlled (product) environments.
This is one of the interesting things about grading sneakers - they're still (mostly) handmade, so you get all kinds of little inconsistencies between pairs. Unnoticeable to most, but easy to spot when you've got two different pairs sitting side by side...