There are actually many varieties of grapes, and the range of colors that they are found in is actually quite drastic.
Many grapes are dark, ranging from black to blue to red to purple. Chemicals in these dark grapes, known as polyphenols, are responsible for the dark color of the wines typically made from them.
There are also many grapes which are lighter colored. Green, orange, and even pink grapes are commonly found throughout the world. Grapes that are actually green in color are sometimes referred to as being white, and are used to make white wines.