Colors tend to be used in programming quite a bit. I'd expect quite a lot of british programmers/techies tend to write grey, even though it's not how it's spelt here. Just as we techies often write 'color' instead of 'colour'.
"Grey" is the usual British English (and Australian English) spelling. "Gray" is the usual American English spelling. http://en.wikipedia.org/wiki/Grey
Don't forget about us Canadians (and all other British expansions), when they brought up Harper on their twitter I started noticing stuff like this, great eye cormullion.