What to KnowGray and grey are both common spellings for the various neutral shades of color between black and white. Gray is more frequent in American English, and grey more common in Canada, the UK, and elsewhere. This pattern extends to specialized terms such as animal species (gray/grey whale) and scientific designations (gray/grey matter). Greyhound, however, is an exception; its grey shares a lineage with an Old Norse word for a female dog.
The color, or really series of colors, that range between black and white can be spelled gray or grey. Both spellings are seen frequently enough to seem familiar, making queries about which is correct very common. Of the two, gray occurs more frequently in American English, while grey is preferred in Canada, the UK, and elsewhere. Both derive from the Old English grǣg.
“Fifteen-year-old Jo … had a decided mouth, a comical nose, and sharp, gray eyes, which appeared to see everything, and were by turns fierce, funny, or thoughtful.”
— Louisa May Alcott (US), Little Women, 1868-9He was a tall, lean man of fifty, with a drooping moustache and grey hair.
— W. Somerset Maugham (UK), The Moon and Sixpence, 1919
'Grey' vs. 'Gray' Beyond Color
The variance in spelling carries over to animal names and other specialized terms that apply the word, such as gray/grey whale, gray/grey squirrel, and gray/grey matter.
Despite the American preference for gray, the spelling grey retains a healthy presence in a lot of cultural references known to Americans, appearing in brand names like Grey Poupon (mustard) and Grey Goose (vodka), both of which originated in France. The titles Grey’s Anatomy (a TV drama) and Fifty Shades of Grey (an erotic novel series by a British writer, E. L. James) have spellings that play on the names of characters named Grey in those works.
The slender breed of dog known for its racing abilities is called a greyhound, and its name is consistently spelled that way. But the name's etymology does not pin that grey on its color; it derives from an Old English word, grīghund, the first part of which is distinct from grǣg and shares ancestry with a Norse word for a female dog.