I'm glad I found this thread. When I started seeing "the dress" all over Facebook, some of the photos people posted looked white and gold, while others looked blue and black. I didn't read the text closely and I assumed people were just seeing/posting different photos (the same photo but with changed parameters, that is). One person even posted two images side by side, one where it looked blue/black and one where it looked white/gold. I didn't get what the big deal was (but then I often don't).
Now I realize you're meant to bring over another person in real life and have them look at the exact same photo at the same time on the same screen, and possibly get a different result. Or, know that you are looking at the exact same photo on the same screen, but at different times, and possibly get a different result. It makes a lot more sense now why people were so interested.