Gray and grey are two different ways to spell the same word to refer to the colour that’s halfway between black and white.
The form gray is mainly used in the USA, while the rest of the English speaking countries prefer the from grey.
The same difference can be observed when grey is used as a verb:
- The inactive fields have been greyed out in the graphic.
- The inactive fields have been grayed out in the graphic.
- I started to dye my hair when I noticed it was greying.
- I started to dye my hair when I noticed it was graying.
For more information on variations in spelling, read Difference Between British and American Spelling.
Grayed out or Greyed out?