my surname is grayson so I tend to use gray, but then I use color now as I do web development and colour:CCC; isn't recognised I don't think btw, I'm English!
both, gray is the color and grey is usually used when describing a noun with the color of gray. example: greyhound
you use the word "colour" anywhere when you're programming or scripting and you will eb getting errors pretty dang sure it is "color" someone understands... gray describes a shade or tone- grey describes a temperement or condition. EG - Technically gray is not a color, but rather a shade. EG - is was a dark day clouds were everywhere, it was rather grey.
programming languages were mostly written using American English. Colour is the correct, English spelling, but some lazy Americans decided to take the us out of some words.
I say we combine them, to make some sort of super colour that spreads across nations...and yes I said "Colour" it looks prettier. GREAY!