Why are most tyres black?

You can get other colors of tires, but they aren't usually available because if the tire is made with the tread actually a different color, they must use different more expensive additives to increase durability. (See Carbon Black answer above)

In addition, on colored tires, the tread portion of the tire rarely looks good for any length of time after being ridden. So customers aren't often satisfied with the product for very long.

Since the same matching effect can be achieved by the sidewalls being colored, most manufacturers go that way instead.

Lastly, most retailers prefer not to stock a tire that is limited in use to only the few bikes which match the tire color. Tires are expensive, and bulky to store. So why fill your wall space with 5 colors of one model of tire, when you can give better service to more customers by stocking one color of five models in the same space.

To protect against ozone and UV damage, a stabilizer molecule called a “competitive absorber” is blended with the tire polymer. Competitive absorbers work by capturing and absorbing UV radiation and converting it to heat which is dissipated harmlessly. All tire manufacturers use the same competitive absorber, carbon black. This is why all tires are black.