Both these spellings are 100% correct and mean exactly the same – a color between white and black. Although grey and gray are correct in English, the former is used in British English and the latter in American English. The difference also applies to species names, for example grey/gray squirrel or grey/gray brain matter.

Definition of gray/grey:
noun, colour between black and white
Grey is James favourite colour.
Gray is James favorite color.


Correct spelling

grey

correct spelling, this version is common in all the other main varieties of english (including britain).

Correct spelling

gray

correct spelling, this version is more common in american english.