In today's (well, technically tomorrow's, in about 10 minutes) review of the Ghostbusters 2 Louis Tully & Slimer Minimates, yo said that the promo photos made "Ecto Cooler" Slimer look like a muddy mess. And yes, that's true, the thing is a mess. But if you compare the prototype to the released figure, the reason becomes clear: there were two separate paint maps applied to the proto.
Look at the image below:
I don't know how a mistake like that happened, but obviously Slimer somehow got two paint apps. Will the one on the right make an appearance someday? Can't say. Is it better than the one we got in the set? That's up to you - just be glad that one of the designs was removed, or else Ecto Cooler Slimer wouldn't have been worth buying at all.