Might as well throw my dark, artistic eyeball viewpoint into this one.
After spending the last 15 minutes exploring the forum in different "lights", I'm a bit torn. Here's my take on each, FWIW:
AM Dark: We're used to it. I always prefer black, but sometimes the contrasting brighter colors and animations used in the ads - both supp ads and the pesky Google ones - is too much contrast. What I like is the "industrial" theme of it, but I can't say that I like all of the rather cheesy brushed aluminum textures used to separate posts and head ever separate box/post/section/etc. It contrasts with the actual background image of the forum too much - horizontal linear vs. a patchwork stamped steel look. It's just a bit much. Still, overall the black color is easier on my blue eyes, which are quite light-sensitive. Yes - sunglasses at night.
AM Light: Again, blue eyes = very sensitive to light. It does make the ads less harsh, but the overall brightness of the posting background is too bright, eventhough quote boxes are shaded slightly (10%?). The ad, banners, and such are all geared towards a black background and would need to be reworked to fit a white one. I don't know if you'd want to go that far - I wouldn't on any of my websites! Overall, the white background looks "cheap" to me. I visit many forums, because I have to, and the standard is always white. You can tell a newbie forum, or a single individual who owns the forum program vs. a corporate entity, by the graphics, layout, and often the skins. White = cheap, IMO. I think AM is much more classy than that.
AM Middle: It's a decent mix of both, but I can't honestly say that I agree with that either. If perhaps the whites were shaded a bit, and the shaded quotes and such were just a tad darker, I think it would be a more happy medium. Instead of being a mix of AM Black's background black and AM Light's thread area white, I'd rather see the "medium" option simply a lighter black or a darker light...if that makes sense. I don't like it being a mish-mash of the two.
Well, that probably didn't help much, but that's how I see things...
Good luck choosing a skin. It won't prevent me from coming back.

:cheers: