gray and grey - the difference

The Quick Answer
If you're following US writing conventions, write gray.
If you're following UK writing conventions, write grey.

Gray or Grey

The colour ("color" if you're an American) between black and white can be written gray or grey.

In the US, the spelling gray is far more popular than grey, and this has been the case since at least the early 19th century. As a result, many Americans consider grey to be a spelling mistake.

Outside the US, the spelling grey (which has been around for nearly 1,300 years) still dominates.

See Also

adverse or averse? affect or effect? appraise or apprise? avenge or revenge? bare or bear? complement or compliment? dependant or dependent? discreet or discrete? disinterested or uninterested? dived and dove e.g. or i.e.? envy or jealousy? hanged and hung imply or infer? its or it's? material or materiel? poisonous or venomous? practice or practise? principal or principle? tenant or tenet? who's or whose?
List of easily confused words