Rolls differences?
 

I've been riding a white perforated Rolls I got on sale at Nashbar a year and a half ago. I recently picked up a used black Rolls (also with the the gold-colored rails and plate) at a bike shop. The white Rolls has a lot more cush than the black one. I'm wondering if exposure to weather could have hardened the foam in the black one - there is some oxidation on the name plate. Or has anyone noticed a difference between white/black or newer/older models with the Rolls?
Thanks!