http://www.martin-missfeldt.com/art-pictures/visual-perception-seeing/retina-rods-cone.php Day 74 has 49 protein-coding genes (browser view), including the gene RHO encoding rhodopsin, the active protein in rod cells that detects dark and light.
Rhodopsin gets its prefix rho from its pink color, which quickly bleaches away when exposed to light. It is most sensitive to blue-green light, which explains the Purkinje effect of perceiving more bluish hues at night. Mutations in the RHO gene can cause night blindness.
Click here to see all 8621546 letters of Day 74, with RHO underlined.