[thaumasiotes]

How are you getting a "theoretical pure black" without having a rigorous theory of color? If you're just going to call some things black and some things red, you'll find that a lot of things that people call black are lighter than a lot of other things that people call red.

[pavelrub]

I’ve already told you what to do if the term “pure black” causes problems. The color represented by #600000 on my monitor is always darker than the color represented by #FF0000, regardless of the existence of any theory of color. If you claim that some formal theory of color convinced you of that, then it would mean that a different theory of color could conceivably convince you otherwise. But this is clearly impossible: We would say that any theory of color which shows that #600000 is lighter than #FF0000 is simply misusing the word “lighter”. This shows that our understand of what “lighter" and “darker" mean is independent of any theory of color, and in fact this understanding is a precondition for the development of such a theory to begin with.

[thaumasiotes]

But none of this is true. #600000 on your monitor might be lighter than #FF0000 on your monitor if they're compared at different times, or if part of your monitor happens to be in the shade. Or if I have a weird viewing angle to your monitor.

If you want to argue about what #600000 and #FF0000 should look like, you're back to a rigorous theory of color.

[pavelrub]

No, because I can be very specific about the condition of my monitor, without reference to any theory of color (I can just say: in the exact conditions my monitor is in at this moment, or in the conditions of a darkened room, where no external light source can make #600000 lighter than #FF0000) . I can hypothetically also show you my monitor in person, in any conditions I choose. In fact I don’t even have to talk about my monitor or those specific colors. We can talk about the color of space as seen from the ISS on the dark side of earth, versus the color of the sun when visible from the ISS. Or the color of my room at night vs the color of a candle flame. There are millions of examples we can think of without talking at all about any theory of color. I mean - it is a matter of fact that words such as “darkness” and “lightness” existed before the invention of rigorous representations of color, and that the numerical definition of those words was designed on purpose to coincide with their existing meaning, and not with some new arbitrary property of color. So I’m not even sure what you are arguing against.

But the whole argument about colors is really unnecessary, I only used it because I thought it would be simpler to understand, but I might have been wrong. If you don’t think that it supports my argument about 2+2=4, feel free to ignore it and address the argument itself.