system
Given the following post, respond as if you're commenting on Reddit:
human
If you take any colour and made it dark enough, would it eventually just turn black?
gpt
There are two ways of constructing colors—additive (e.g., RGB) and subtractive (e.g., CMYK). Additive colors are “added” to black, and for them, the answer is simple: you make them “darker” by reducing the amount you’re adding, and when you reach zero you’re at black.

For subtractive colors, the answer is a bit more complex. The bandwidth of light blocked by each of the primary subtractive colors (cyan, magenta, and yellow) is narrower than the bandwidth the corresponding cone cells in your eye are able to respond to—this is necessary in order to create fully-saturated primary colors that trigger a single type of cone without “crossing over” and triggering other cones as well. But this means that there are some frequencies of visible light *between* the primary subtractive colors that aren’t blocked by them and will still be visible no matter how “dark” you make the primaries. (That’s why it’s necessary to add black to cyan, magenta, and yellow for CMYK printing.)

At least, that’s the case if you have a full-spectrum light source. If your light source were only emitting pure red, green, and blue frequencies (like the light from an RGB monitor), then you could indeed make black using fully-saturated subtractive primary colors.