This is an interesting article on how anthocyanins affect pigmentation in blood oranges. 
The actual ancestry of Sicilian blood orange variety is also being discussed in the accompanying video.
 http://news.jic.ac.uk/2012/03/blood-oranges/
http://news.jic.ac.uk/2012/03/blood-oranges/
By the way, this guy's got some really strong accent... 

 does anyone think the same?
Enjoy the article!