Natural rubber is a white, organic product, which is harvested in the form of latex from rubber trees. The latex itself is a sticky, milky sap which is “drawn off” by making incisions in the tree’s bark and collecting the fluid in vessels in a process called "tapping". The latex then is refined into rubber that is ready for commercial processing.

Rubber is used extensively in many applications and products, either alone or in combination with other materials. Although it is an incredibly useful and versatile material, it’s not terribly tough in its natural state. For it to endure the heavy-duty wear of daily use, for example, on a car tire, it needs help.

Originally, tires were an off-white color (due to the natural color of rubber). They also had a much shorter lifespan, usually less than 5,000 miles. (By comparison, most tires today are driven between 12,000 and 15,000 miles a year, for three to four years, essentially lasting 10-12 times as long.)

Rubber that “hits the road” today is made black by adding a substance called carbon black, a fine manufactured soot. This isn’t just for cosmetic reasons (like not showing dirt). Adding other substances, like carbon black, adds desirable qualities, such as durability and strength, to the rubber.

More Info: en.m.wikipedia.org