I am left wondering at what other apparently physical phenomena are invented by our mind in order to create a continuum.
I would guess all of them, in this sense: In the process of making them understandable we leave out what we don't immediately understand and shape everything else to make it comprehensible, or in the sense that whoever got there first created the structure and often that first structure sticks. You think?
I suppose so. Here we have a physical point of reference, the visible spectrum, but map our non-spectral color experience upon it, creating something that doesn't exist, but perhaps is easier to comprehend. I don't even know if that is the case. I've always considered purple and violet to be pretty much the same thing and never thought much about, although it's obvious they are not. And what the hell is indigo? But of course, all these basic color choices are arbitrary. I don't know if the color wheel does make it more understandable at all. Is happy the opposite of sad, or is it actually the opposite of ennui, and we have just grown accustom to speaking about it that way?