Butterfly or Moth?

Just back from Dunkeld where i spent the weekend with the landscape photographer Colin Prior who i was giving some tips and advice to, to improve his photography.

Spotted this little fella, topping up his tan at The Hermitage. Is it just me, or does it look like he's got shades on?

I've never seen a butterfly/moth like this before, it was completely green, with almost no markings.