Humans are used to seeing red in blood — but red blood isn't universal in the animal kingdom. For some creatures, this vital fluid is purple; in others it’s yellow, green or even white. Smithsonian Magazine spoke with John Postlethwait, a developmental geneticist in the Department of Biology about Antarctic blackfin icefish of the family Channichthyida, the only known vertebrates that don’t make hemoglobin and do not have red blood cells. Their blood is a milky, translucent white. “They really are kind of ghostly," he said.