Many animals have red tongues, though not all of them - blue-tongued skinks and giraffes come to mind. Are they red because of the blood (and therefore haemoglobin) in them?

It sounds plausible, but it also sounds like a post-hoc explanation.

I'd be especially curious about any other species having blue blood, like horseshoe crabs, but still having red tongues, unlike horseshoe crabs, which apparently don't even have tongues.