Blood oranges are believed to have originated in
Sicily sometime between the 17th and early 20th century. No one is sure where the red came from in these fruits, and it's generally chalked up to just a random
mutation that sprang from sweet "dessert"
oranges that were imported in the 14th century. Sicilian blood oranges are still regarded as the
best in the world, but blood ornages have since been cultivated in
Spain,
Florida, and
California as well.
The red color, which blushes or bruises on the skin and marbles in much deeper shades irregularly through the meat of the fruit, is caused by anthocyanin, which causes red and orange shades in fall leaves and is also present in some other vivid red fruits. Apparently, this color on the fruit is affected, among other things, by the climate. If cold nights and warm, bright days are not present the red color may not develop on the fruit, although the taste is not affected much. As for the taste, it's far sweeter than most oranges and many people say it has a berry--raspberry or strawberry--overtone to the normal citrus taste.
http://www.foodreference.com/html/fbloodorange.html
http://www.produceoasis.com/Items_folder/Fruits/BloodOrange.html
http://www.watchtower.org/library/g/2001/2/8/article_01.htm