Before you go buy paint, you need to look at the damage.
is it a scratch or a chip. can you see the primer?
If it's a scratch, try a remover first. Scratch X by Meguiar's is great (when sed properly). Run the back of your fingernail over it. If you can noticably feel the scratch with your fingernail, you won't be able to remove it with scratch remover, but it can reduce the appearance