I’m so confused. This is something people know? I mean, I can work it out from first principles knowing how color mixing works, but it sounds like people just … know them?
I’ve been programming for almost 40 years and it would never have occurred to me to memorize this sort of thing.
I doubt anyone has many of them truly memorized. It's more like having the ability to quickly see each hex character and understand roughly what percentage that is, then quickly visualize the resulting color. My methodology playing this is to just convert each hex character to high, medium, or low, so you end up with something like "high red, medium blue, low green."
The typical sets of primary/secondary colors are RGB and CMY. Which set is considered "primary" depends on if you're doing additive (light) or subtractive (ink/pigment) mixing.
In additive color mixing, Red (#F00), Green (#0F0) and Blue (#00F) are the primary colors, and Cyan, Magenta and Yellow are the secondary colors.
You also need to know the combinations, for when you get, eg, 0FF. Though I was once asked to find 0FF and the choices also had 1FF in them. Obviously it was pure luck.
Just know them no. Able to sanity check that an RGB value is the color it's supposed to be yes sometimes. It's not the most useful skill because you almost always get a swatch now, but sometimes being able to have some idea of how it'll look (should it be dark or light, grey or intense color) saves me 10 seconds here and there.
I like playing guess-RGB games every now and then because it improves the skill, but at the same time I find them really stressful haha.
More like being able to naturally parse the base 16 value without thinking about it, just like you can parse which of these numbers is bigger without thinking: 4 8
And then having a natural intuition for how the relative mixing of color values should look.
I’d say you could do pretty well if you took your time and thought analytically about it, but some people have just developed a strong intuition for it.
This would be much harder if there was a “none of the above” option.
>I mean, I can work it out from first principles knowing how color mixing works
did you try it? if you can work it out from first principles because you know how color mixing works, you should get a perfect score; that's the game. If you don't get a perfect score, you need to reinspect what you think you know about color mixing and even the first principles.