Goal: Rather than changing the color of the prompt, I would prefer to change the color of things I type in. I strongly believe in using the <kbd> tag to visually separate input from output.

What methods exist to do this?

Bash — source code

It might be possible to create a patch for the Bash source code.

Bash — using DEBUG trap

see here

ZSH

YES, this is possible in ZSH. ZLE (the line editor) has the capability to load third-party widgets. These widgets can trigger off of specific things, including: