Anodised aluminium does seem to mark very easily in my experience of Apple gear over the years.
Slap an iCarbons skin on the back

I put a "titanium looking" one on the back of mine and it helps protect it from everyday "putting it down on a table" kind of scratches, looks nicely metallic so it still looks premium, doesn't show up fingerprints, and adds no appreciable thickness so it works with things like the Logitech ultrathin keyboard. Very glad I went with this approach instead of a full-on case/cover.