Actually, tires were black. After a while would get a gray tinge on sidewalls, bit of grey inside treads. where tires touched the runway, were always black, usually new layer would be burned off at landing (which explains the bit of smoke and those nice stripes on a perfectly clean runway.
SR-71 tires were dull aluminum, bit of bright silver on edges, discarded after 3 flights.
we did a bit of back channel horse trading with China Lake. They used A-7s for pilotless drones, they'd get our crap tires, we'd get their newer ones for our flight test A-7. Same with lots of other equipment. At the time our company was still subsidiary of LTV which built the A-7.