Pure Grey is sadly not available on a Highline, but it is a stunning colour.
If it's a Highline, then it should be Starlight Blue and Indium Grey.
Starlight looks lovely in the sun all detailed up, but Indium is a very popular colour that will have a more desirable re-sale.
Then Indium is so popular it's hard to make one your own, without it looking like another one, the Blue is a little easier in that respect.
Neither are colour i'd choose personally, but out of the 2 if they are your favourite colours, i'd be flipping a coin, or digging through each Team on here to see what looks best with any future mods you might intend on carrying out. (or not)