I had heard that you can dye skateboard wheels using a packet of Rit, so I gave it a shot on an old set of white wheels–yellowed with age:
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Prep the wheels

I sanded the remaining silkscreen off of the outer rim, washed the wheels, then gently sanded some of the darkened surface of the wheel. (I later determined this surface sanding is probably unnecessary)
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Prep the dye bath
I filled a medium sauce pan with water–just enough to cover the wheels–and set it simmering on the stove. I then emptied a full pack of Rit dye (I chose Royal Blue) and a quarter cup of salt into the pan. (I now wonder if less dye would result in a brighter or lighter color.)
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Dunk the wheels

I set the wheels in the simmering brew, and stirred them for about 20 minutes. (Again, I wonder if for a brighter or lighter color 5-10 minutes might work.)
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Remove, Rinse, Dry

Ta-da! (These are actually much darker in real life than they appear here, thanks to the camera flash.)

