Any of the photopigments in the retinal cones and rods that absorb light and photochemically initiate the phenomenon of vision.
Grey vs. GrayGrey and gray are both accepted in the English language. They refer to a color of a neutral tone between black and white, and can also be used metaphorically to convey gloom and dullness. However, gray is the more popular spelling in the US, while grey reigns supreme in the UK. For centuries, the one letter difference between gray and grey has left people wondering …
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.