Out of curiosity, what compelled you to choose those colors and purposes for the Zener symbols? Circle and Cross are the standard yellow and red, but the rest being nonstandard is interesting.
I can hazard a guess that green for Stars didn't hit the vibe of 'emotive and enigmatic noises', and that change informed Waves being spring green instead of blue, with Square being a more informative/mechanistic steel grey by necessity, but these are all total presumptions.
An unofficial standard as far as having the symbols printed commercially in color, at least; it's understood that adding color to the cards is a modern twist.
When they do show up in color, the color scheme that shows up on Wikipedia seems to be the most common (with some variations), and the earliest reference of that colorscheme seems to be 2008 on the site itself. So it's likely a case of Wikipedia informing an unofficial commercial standard.
Either way! It'd be interesting to hear the thought process on the symbols' colors and meanings, even if it ends up being not that deep. 'They just felt fitting' can be fascinating in its own right.
Here's what I could reconstruct from notes from two weeks ago me.
