The real dress IS black and blue.

There is an objective, verifiable, measurable answer. How we perceive reality might indeed, at times, be distorted, but people who say "black and blue" are, at the end of the day, objectively correct.

The erroneous conclusion many people took away (both back in 2015 and, indeed, even in the comments here) is that subjectivity somehow makes all of our perceptions equally valid, whereas, in reality, one group's "subjectivity" is an accurate reflection of the material world and that of the other group is not. Not all opinions are equal, some people have better, more accurate perception than others so framing this as "we disagree, hence, all of our justifications are epistemically equal" is factually incorrect.

Our brains may construct what we see and, at times, it might indeed be wrong, but some people's brains are simply better (be it due to genes, early exposure, training, a combination or something else entirely).

Cheers.