Would be yellow, no? Yes, but you could put these nifty white plastic wheels on anything you like. You've seen lawnmower wheels? That's what these are like. Measure 6" dia x 1-7/16" thick with hard black rubber treads, a 1/2" axle bore and a 13/16" x 1/4" hub on the opposite side.

If these were full-size, car guys would put them on restored ’57 Bel Airs and low riders. These 6” dia solid rubber wheels are gray with (5) treads on 1-7/8” wide tires. Mounted on a 4” dia aluminum rim with dual 9/16” ID bearings with a loose bushing between them. One side has a nearly 1-3/4” dia hub that protrudes approx 3/16”; the other bearing is recessed by 3/8”.

For your riding comfort, this 9-5/8" dia x 3" wide pneumatic tire has a plastic hub, rubber treads and a 25psi inner tube. Has a 1/2” ID with a 1-1/4” dia x 15/16” axle hub on the inside face and a standard Schrader air valve on the outer. Great for DIY large wagons, or to replace those little hand truck tires.