Carrots are orange for entirely political reasons: in the 17th century, Dutch growers are thought to have cultivated orange carrots as a tribute to William of Orange – who led the the struggle for Dutch independence – and the color stuck. A thousand years of yellow, white and purple carrot history, was wiped out in a generation.
Although some scholars doubt if orange carrots even existed prior to the 16th century, they now form the basis of most commercial cultivators around the world. Presumably crosses between Eastern (purple), Western (white, red) and perhaps wild carrots led to the formation of the orange rooted carrot sub species. Turkey is often cited as the original birthplace of the hybrids (or mutations) of the two groups.
Whatever the origins, the Long Orange Dutch carrot, first described in writing in 1721, is the forebear of the orange Horn carrot varieties so abundant nowadays. The Horn Carrot derives from the Netherlands town of Hoorn in the neighborhood of which it was presumably bred. All our modern, western carrots ultimately descend from these varieties.