Orange carrots are known to detoxify the liver and improve eye sight, however new studies demonstrate black carrots can play a significant role in protecting against colon cancer.
Carrots are one of the few crops that are available throughout the year. They not only come in bright shades of orange, but also deep purple and even black. According The World Carrot Museum, black carrots are believed to have Middle Eastern origin. During the fall, carrots are considered to be in season and they are the freshest and most flavourful.
Long before the orange carrot became established in the 16th century, the black carrot (Daucus carota ssp. sativus var. atrorubens) existed across in Asia and the eastern Mediterranean. Black carrots are still grown and consumed in Oriental countries such a Turkey, Afghanistan, Egypt, Pakistan India and the Far East.
Wild carrot has a small, tough pale fleshed bitter white root; modern domestic carrot has a swollen, juice sweet root, usually orange.  Carrots originated in present day Afghanistan about 5000 years ago, probably originally as a purple or yellow root. Nature then took a hand and produced mutants and natural hybrids, crossing both with cultivated and wild varieties. It is considered that purple carrots were then taken westwards where it is thought yellow mutants and wild forms crossed to produce orange. Finally some motivated Dutch growers took these mutant orange carrots under their horticultural wings and developed them to be sweeter and more practical. Black carrots are more weather sensitive and it is suspected that they did not “travel” well to the colder parts of Western Europe. Even today growing black carrots in the West can be problematic and they often bolt in the first year, producing spindly roots and no, or weak flowers.
Black Carrots contain anthocyanins, part of the flavonoid family with antioxidant properties. Flavonoids are currently under investigation as anticancer compounds, as free radical scavengers in living systems, as well as inhibitors of LDL (the bad) cholesterol and the black carrot anthocyanins are especially active.
***Source: Fresh Plaza (additional information from Carrot Museum http://www.carrotmuseum.co.uk)