(gold is FFD700, defined by HTML standards).
HA HA HA! YOU FELL INTO MY TRAP!
Pardon my caps, but I set a lot of these, and they are rarely stepped in so beautifully. That's my fault, of course. But, here we go.
When you hear the name of a color, you think of some color which you associate with that, or a thing which you think of as being that color which actually has a whole texture, reflectivity, depth, etc. But the truth is that the same name is being used right now by a dozen different paint companies to describe a dozen different colors, which are then described in thousands of different ways by the downstream users of the paint. There are some absolute color standards based on elements, oxides of the same and the like, but even those are frequently "abused". The truth, though, is that outside of a small handful of colors, they are not defined by any unifying principle. Your use of the HTML standards is particularly hilariously perfect, I really hope that you meant to put your foot there! Outside of web design, nobody but nobody gives a crap about that. Before that, we had the X rgb.txt file, which nobody outside of X-land cared about, which begat HTML colors by the way, junior. But meanwhile, over in the land of professional color, there were multiple competing color standards including AGFA and Pantone — and there still are.
It's interesting that part of this debate is also over the color "black" because "black" is what you see when you don't see anything, and if any part of the dress were truly black then the photograph would look like an editing mistake. Even the color black is subjective. That should be intuitively obvious to a web designer (who else would even mention HTML colors?) who has to deal with the real-world effects of differing black and white levels all day. I may be sitting at a monitor with 120% color (Adobe gamma) but I don't expect other people to have them. As far as I know, there is no color correction e.g. for Android which is not manual, and then the color adjustments become utterly perceptual.
I suspect that celebs are adept at perceiving the actual color of the dress because they have appeared in so many washed-out photographs.