I managed to see the black and white version. Bong said it would highlight the actors' performances. I might agree.
I came away from seeing the black and white version feeling a little more sympathetic to the Kims, especially the father, than I did the first time I saw it (in color). I can't necessarily attribute it to the black and white, but I think the scene of them returning to their flooded apartment, and the next one where they were in the gymnasium/shelter, were very effective in black and white. The image of the father's face while lying in the gym really got to me.
Not as effective was the scene where he puts hot sauce on the tissue, to make it look like the housekeeper is coughing up blood. And there were other scenes that I'm sure would have been lit differently if the movie was shot in black and white. And of course you completely lose the green yard at the Parks' house, which really is a loss.
I was surprised at the size of the audience when I saw it. There had to be 25 people there, at 1:45 on a Friday afternoon. I do wonder if all of them realized what they were seeing, since only certain screenings were in black and white, and you had to dig a little to figure out which ones. When I bought my ticket, the clerk didn't say, "Just so you know, this is the black and white version."
I wouldn't be surprised if people who knew about it only because of all the awards could see the black and white version and not realize it's not the original version.