Quoted from djreddog:
My first thoughts were the box was simply wrong because the invoice and the paperwork was all correct. However, after opening the box and seeing a purple game I knew at that moment it was in fact a premium and made the decision to contact the distributor first thing Monday morning.
That was cool and considerate of you, but if you're shipped something you didn't order FTC says you can keep it. I'd see what the Dist offers and work toward a win-win discount so he's not totally screwed and you don't pay more than you thought you were going to. You did something you legally didn't have to do by calling him, which he should appreciate.