Did you know that not all blood is red? While most vertebrates (like humans) have red blood, octopuses and crustaceans have blue blood, leeches and some segmented worms have light green, lizards have green, some marine worms have violet, and sea cucumbers and some beetles have yellow! Write in the rainbow of blood colors with this gel pen 6-pack. .7 mm tips Each pack contains 6 unique colors: Hemoglobin Hemocyanin Chlorocruorin Hemerythrin Vanabin Biliverdin