i swore off buying oil in a clear bottle after working at K-mart and helping out in the auto department.
all products get stocked from back to front, with the oldest product up front. the quaker state in the clear bottles wasn't a hot seller so it took a long time before it needed to be restocked.
after 6 months, i finally put some out and all the bottles in front were noticeably darker than the bottles i took out of the box.
yeah yeah yeah ... color means nothing ... but sitting under the UV from the florescent lights 24/7 for 6 months did *something* (yes, they never shut the lights off - cleaning crew at night)
if you buy oil in a clear bottle, make sure to grab it from the back so you get the new stuff, or ask them if they have a box.