Yes, this is about that dress. I really think it’s over-discussed, but since some people still don’t understand how it works, I’ll try to explain as simple as I can. As can be expected, XKCD’s illustration is very simple and easy to use for demonstration:
Colorpicking on one of the dress’ colors and then brushing a bridge between them shows that they’re exactly of the same color:
It works almost exactly the same way as this popular optical illusion (explanation here for the curious):
The difference is that in the dress picture there’s not enough background color for reference, so our brains make assumptions of the dress’ surroundings. Those whose brains assume dark background/ambiance will see white/gold, while those whose brains assume bright background/yellow radiance will see blue/black. These assumptions are made subconsciously. It explains the hardcore extremists: you believe that what your brain assumes is true; and it explains how one can see it differently from time to time: your assumptions can be influenced by things such as the real environment that you’re currently in, or even your mood.
As an (self-proclaimed) artist who’s used to working with colors, I’m (self-)trained not to make this kind of assumptions. When I was asked what color the dress is, I answered with what my eyes objectively see: the face value of greyish blue and brown, as the HSB values below prove. The colors in the picture (not of the actual, real-life dress) are neither blue/black nor white/gold. They are greyish blue/brown.
Well I hope that makes it clear and no friendships or relationships are hurt because of it.