From skating a lot on a certain ramp painted red from a long time ago now, it didn't matter what colour (white) the wheels were they would always end up this weird orangy colour from the ramp.
That is more my Spitfires than another guy who had Bones wheels, but I have seen other brands do this too, depending on formula, eg usually the more milky translucent coloured wheels would absorb the terrain colour more so than the bright plastic looking white wheels, that never seemed to change colour.
I have Bones STF wheels that are still new in package, from maybe ten or more years ago that are still whiter than anything that is coming out now, including those 99s and other ones that I bought some of, which are new current stock. The SPF wheels from the same time also still new in pack are more yellowed than new natural F4 Spitfires, so it always made me wonder what goes into the formula of the wheel that would have such a lasting effect on the colour.
Older Spitfires in classic formula go almost dark brown over time, along with some that go pinkish brown and another set that have gone greenish brown, all still new in packaging and kept out of light, so go figure. Anything under fluorescent shop counter lights or direct sunlight usually went off colour very quickly.
It might be fun to lay some out and take pics of them to compare, when I have a minute.