It's not paint, it's an anodised coating that you'll be unable to replicate at home. The best advice is to just live with it, as most likely any 'repair' will only accentuate the scratch and make it look much worse that it is. Once a little dust gets in there it'll darken down and won't be too bad.
If you really wanted to use paint on it, you'd have to find a similar anthracite colour, carefully dab it on then wipe the excess, leaving only a tiny bit of paint inside the scratch. But do that at your own risk, depends how experienced you are with these sort of things.
