Grey is how to spell the color Grey, when I was in elementary school so I voted for the correct spelling of the color,
according to the internet in the US it's spelled Gray not Grey. But from what I remember growing up in childhood school even in the United States in the 1990's the color was spelled Grey. But that old school though
thats just my 2 cents
I could have been reading outdated books though. I mean this was back in 1993-1995 when I first started spelling this was before the internet became bigger
goggled it and came up with this below
Grey is the dominant spelling in European and Commonwealth English, although gray remained in common usage in the UK until the second half of the 20th century. Gray has been the preferred American spelling since approximately 1825, although grey is an accepted variant.