Nomenclature
Annoying, isn't it? Took me a few seconds to realise what they were, the skin colour helped.
I think this may be a UK thing. In Southern Europe they seem to be less squeamish. In Portugal and Italy their name for these things seems to be comprised of the local words for blood and orange.
Incidentally, why hasn't some boffin/plant-breeder developed a blood orange that is as easy to peel as a tangerine?