The Wikipedia article (link in an earlier post) doesn't mention blood oranges, but says this:
'The flavonoid existing in highest concentration in grapefruit juice is naringin, which in humans is metabolised to naringenin. There are also other flavonoids in grapefruit juice, in lower concentrations. Orange juice does not contain naringin in as high a concentration, instead containing hesperetin. It is sometimes recommended as a substitute. Juice of limes, and Seville oranges and apple juice can also inhibit metabolism of some drugs.'
'The flavonoid existing in highest concentration in grapefruit juice is naringin, which in humans is metabolised to naringenin. There are also other flavonoids in grapefruit juice, in lower concentrations. Orange juice does not contain naringin in as high a concentration, instead containing hesperetin. It is sometimes recommended as a substitute. Juice of limes, and Seville oranges and apple juice can also inhibit metabolism of some drugs.'