Answer: White

Although it would be easy to assume that the deep black color of modern tires was simply the color tires have always been, the earliest tires were completely opposite in color. Before the introduction of carbon as a preservative and stabilizer in the early 20th century, tire rubber was a semi-translucent white color that looked quite similar to a gum rubber eraser.

This is also why the Michelin Man, iconic mascot of the Michelin tire company, was depicted in white–a color as far removed from the inky black of modern tires as you can get.