VA few years ago, a photo of a striped dress was circulating on the Internet. The question of its colourfulness divided the world: for some it was white and gold, for others it appeared blue and black. Neither party could imagine that there was another point of view besides theirs.
We all assume that what we see is reality. We consider our perception to be an image of the objective outside world. In fact, this supposed reality takes place almost exclusively in our head. It starts with color vision: while I am working on this text, a bright red coffee cup stands in front of me. But since Isaac Newton we have known that colors do not actually exist.