I don't choose anything; I just use the xterm defaults. Some colours inherently conflict. Blue on white is fine. Yellow on black is fine. Yellow on white is not. White on white is even worse. There are many combinations that don't really work brilliantly. Some applications set background colours, some don't. pamix, ngrok, and npm are examples of applications that hard-code background colours. Configuring the terminal to use text colours that work well with both the default white and hard-coded black (for some applications) is hard.

That I need to spend a bunch of time setting all of this up (among other things) is exactly how this thread started.