Erythrophobia could mean "fear of the color red." Carl Sagan mentioned in a book he wrote that elevator buttons are often labeled green for UP and red for DOWN. He conjectured that this choice follows from our arboreal past that we spent swinging from branch to branch. Up was good. Up was where the leaves were. Leaves are green. Down was bad. Down was where the ground was. Down meant falling out of a tree and getting injured. Injury was associated with blood. Blood is red. Erythrophobia could mean "fear of blood" or "fear of injury."