A little OT, but had to google the english spelling and it seems that for the color, 'grey' is the dominant spelling in the U.K. and the Commonwealth, while 'gray' has been the dominant spelling the U.S. (since ca. 1825). I find the latter odd, as I was taught by American teachers only to use 'grey' for the color.
This is quite odd since I am American, yet I spell the color "grey". My friends spell it "grey" as well with few exceptions. I associate "Gray" with like a personality (dull) and or last names. Besides, phenetically "Grey" makes more sense, "ey=strong a (Like "Fate"), so therefore Grey", however "ay=strong I (like "I"), so Gray, if phonetically correct would sound like Gri"
<rant> I agree that 'grey' should be the correct spelling, but I think both spellings should at least be pronounced the same (Hey, if you stay, you may pay for the whey, okay?) There are key exceptions, though (ha!). I always associate 'gray' with the actress Linda Gray from 'Dallas', and it has served as a life-long mnemonic for me that it is not the way to spell the color. </rant>
"Utenfor" is used for specific issues. It would make more sense if you specify where one is outside. For instance: "Det er grått utenfor butikken", "Det er grått utenfor huset hennes", etcetera. Your phrase isn't completely wrong, but it sounds extremely weird without a context.
I think we should let the title of the "beloved" book decide: "50 Shades of....:)....kidding, I have no idea, but I have always used "gray" so now I feel kinda torn up about it. I may have to switch....Minnesota rural school education of the early 80's be damned!!....but to all of you bullied students of "old school," angry teachers out there....I DO feel your pain all the same...sigh