Sounds like the problem is not colors, but the amount of stuff we're differentiating then. You could say the same thing about making things bold, italics, shades of grey, etc.

I would think people recognize different colors better than shades of grey or bold text though.

Interestingly, in a lot of Japanese advertisement it feels like all the ways of making something stand out have been exhausted.

To my brain, syntax coloring makes recognizing the shape of some code a more rapid/fluid process. It also provides a nice feedback loop for potential typos (in my cli setup, a misspelled command will be red instead of green, a string will be yellow, etc) so that you can catch an error before you execute/commit.

Outside of all of that, I enjoy the rainbow festival aesthetic. I coded a lot as a kid for fun, and was good at it, but got away from it as an adult. I think a huge part of transforming back into an enthusiast was all the attention to themes, fonts, ligatures, autocompletions, etc. I really enjoy "talking" with my computer, and all of the styling gives a sort of pseudo-personality, as the computer responds to my syntax with different colors as I'm writing it.

That said, you might not like rainbow personalities! That seems to make you an outlier, but it doesn't matter! One great thing about code is that it can be easily adapted to a users preferences...that is, as long as you're using tabs for indentation and spaces for alignment ;-)

It’s a good thing we can adapt it to our taste, then.

Differentiating by, and extracting meaning from, color is a very ancient and important part of our visual system and every day life. Why wouldn’t you want to take advantage of it, living in a black and white world?