Small 3x3x3 color cube with 5-value grayscale ramp, from ANSI 256 VT colors
asciinema.org
asciinema.org
I've seen people do wonderful things with four colors only.
If you split up the rgb cube evenly you wind up with many shades of green that are somewhere between "makes me want to puke" and "this is what you see when you get hit with a green laser pointer."
That was misunderstanding the application, for sure.
Here is what a physicist would probably do to test that 3x3x3 thing: https://imgur.com/gallery/6HOORem