Is hair grey or gray?

Whether hair is spelled grey or gray depends on which regional spelling convention you are following, as both are correct but used in different countries. If you are writing in American English, the standard spelling is gray hair, with an A, and this is the form used in American dictionaries like Merriam-Webster and style guides like AP Stylebook. So you would say he is going gray or gray hair. If you are writing in British English, used in the United Kingdom, Ireland, Australia, New Zealand, Canada, and other Commonwealth countries, the standard spelling is grey hair, with an E, as preferred by the Oxford English Dictionary. So you would say grey hair or going grey. Both spellings refer to the same color, the silvery white that hair turns with age due to loss of melanin. In proper nouns or brand names, the spelling may be fixed, such as Grey Gardens or Grey's Anatomy, which use grey regardless of region because it is part of a name. For general descriptive use, choose gray for an American audience and grey for a British audience. Many people remember it as grAy for America with A, and grEy for England with E. Either way, both describe the same hair color change.