ugh, that sucks that it's large. Well, what you could try to do is find a program (i know photoshop does this, but most people don't have it around here) that can select similar colors over the entire composition. I would have to say that those boxes are all one color since they're all affected by the transparency. So highlight one and then auto highlight them all, click delete (no antialias) and save as a png. You should be good to go.