Grey and gray are two different spellings of the same word. Gray is more common in the United States, while grey is more common in other English-speaking countries. In proper names, the dog breed greyhound, the unit Gray, and the grayling fish, the spelling always stays the same.
As a noun, gray usually refers to the color. It can be used as an adjective when we want to say that the color of something is a shade of gray. It can also be used as a verb, for when something turns gray. But regardless of its use, you’ll sometimes find that gray is not spelled the way you think it should be. Or, you might be reading this and thinking “those people at Grammarly really don’t know their spelling—it’s grey.” So, what’s behind the grey/gray dilemma, and is there any difference between them, besides the obvious?
Gray vs. Grey—What Is the Difference?
Does your vowel choice really make a lot of difference in the case of the color gray? It doesn’t. The spelling doesn’t affect the meanings, and both spellings are perfectly fine when writing about the color between black and white. The pronunciation remains the same regardless of the spelling you’re using. In fact, both spellings have the exact same origin.
The only difference is that gray is more common in the United States, and grey is more common in the rest of the English-speaking world. So, you can write:
But you can also write:
It doesn’t matter whether you’re using the word “gray” as a noun, adjective, or a verb. You can say that someone’s hair has grayed over a couple of months, but you can also say that it greyed. Things can be greyish, but they can also be grayish.
Grey and Gray—Are They Always Interchangeable?
In common usage, there’s no difference between the words grey and gray. Some people might believe each spelling refers to a different shade of gray, and it’s quite possible you’ll see this in practice when looking at color swatches.
But there are a couple of cases where you really should mind the vowels. One of those cases is greyhound, the dog breed. It should always be spelled with an e, not an a. It’s the other way around for the grayling, a species of fish with a name that’s always spelled with an a.
If Grey is someone’s last name, you obviously shouldn’t change it to Gray to match the way you think it should be spelled. Proper nouns are off limits—the vowels in them cannot be changed. And neither can the vowel in Gray, the unit for food irradiation—it’s always spelled with an a.
from Grammarly Blog https://www.grammarly.com/blog/gray-grey/