I had this same issue, and I was never able to get it working. I'm sad, because I would love to play, but I cannot.
People keep saying to change the color-depth, which you cannot do on latest versions of a mac, and nor should you need to. I realise the problem may not be the Devs fault at all, but it is a critical bug for anyone on an OSX laptop (not sure if it affects external monitors), since we cannot play at all. They should figure out what WE need to do, and put up a guide, if it is not something they can fix on their end.
They will get very few mac users, because the game doesn't work out of the box on macbooks, and most people aren't going to bother coming to the forums to look for a solution. (which no one has gotten, I may add). I am quite a technically savvy person, and even I can't figure it out. I even tried to download external 3rd party programs to change my color depth, which didn't work either. I've looked at every thread on this topic, and some go back many months. No one has had success from what I can see.
I would love to see a real solution to this problem, because I want to play this game, and I want to give them my money.
For the record, the game did use to work, I played years ago and it worked fine. I believe the issue may lie with macbooks, or the retina display, but i'm not sure. I don't have an external monitor at the moment, or i'd try hooking it up and see if it worked.
anyhow, just my rant.
