Which is correct, the "grey" or "gray" spelling?

Have you often wondered "Am I spelling g-r-e-y correctly...or is it g-r-a-y?". How do you spell the color grey or gray?

A bit retarded when I can't spell "grey" or "gray". I mean, they're both correct lah. Then I goggled..

"Gray is used primarily in the United States and other areas that use US English. Grey is used in Great Britain and areas that use UK English."

THERE! Totally solved my doubt. Obviously we use gray GREY (for Iris' sake) here (in Singapore) but I've found interesting way to remember it!

grAy is how it's spelled in America
grEy is how it's spelled in England 

Well, the only exceptions are:

1. Proper nouns such as a last name; Earl Grey and Zane Grey would not be spelled Gray and L.H. Gray must be always be spelled Gray.

2. Greyhound as in the dog breed.

Here's a handy chart.