Some fans theorize it's Unicorn blood, which is likewise silvery in color; however, given how all ghosts of Hogwarts have a silvery hue this may be a coincidence.
It's Unicorn blood. This is what some fans theorize. Unicorn blood is likewise silvery in color. This may be a coincidence. This is however. This is given. All ghosts of Hogwarts have a silvery hue.