The picture was 'obviously' light blue and gold - to me. I assumed the people who saw black and blue were somehow processing the white balance in their heads, which is pretty damned clever. It's as though they weren't seeing what color the picture was, but estimating what color the real dress is and reading it back without realizing that's not what was on the monitor. The real dress is, equally obviously, blue and black.
So this morning I checked in Photoshop. (Yes, I'm still wasting time on it.)
The original picture, slightly ensmallened:
What the picture looks like in a Photoshop window (you can see Photoshop just says, 'open', i.e. it's done nothing to it):
Taking a sample of "white" or "blue" in the dress with the eyedropper:
The little circle in the color palette shows what color Photoshop thinks the blue or white area is. It's not white, is it? It's a light blue.
Taking a sample of "black" or "gold" with the eyedropper:
The little circle shows what color Photoshop thinks the area behind her right shoulder is. It's not black, is it? The original picture has gold (or orange or brown) on the lace strips, depending on where you sample.
White balancing the picture by hand (taking the color cast off using adjustments):
Once you adjust the picture for the overexposure, it's blue and black. I adjusted the color under
White balancing the picture under adjustments using the eyedropper to set white, black and mid-range in the areas outside the dress:
Instead of using my eye to take off the color cast, I used Photoshop's eyedropper tool on the areas outside the dress - white, by her right elbow, black by her left hip and grey at the far right past her elbow. It's actually quite a pretty-colored dress when it's color balanced!
(I think I've got some clipping going on there, but that's enough on the dress for me today.)
Edit to add: scrolling the small pictures up my monitor on the finished post shows all of them gradually changing from bluish-goldish to blue-black as they ascend. It's freaky.)