It's not as easy as you might think to track down blood oranges, but I managed, it, and spent an afternoon juicing and chopping and boiling.
I ended up with 6 and a half jars.
It's pretty, although not quite as pink as I had hoped, based on the juice.It's also much sweeter than the ordinary Seville kind, so I shall probably use it for baking, or to offer to guests, as I like my marmalade pretty tart.
For comparison - Blood Orange on the left, Seville Orange on the right.
I also bought some pin grapefruit and am planning to make a small batch using those, too, to see how that turns out.