The background highlighting when pasting text into into the terminal / shell has subtly annoyed me for a while. Here is how to remove it:
zsh: Add `zle_highlight+=(paste:none)` to ~/.zshrc [1]
bash (v4.4+): add `set enable-bracketed-paste off` to ~/.inputrc [2]
[2] https://www.garyshood.com/bash-highlight/