I’ve been using kitty and tmux together for years and recently realized my setup for true colors was broken, thanks to neovim’s :checkhealth command. After some searching and trial and error, the setup I ended up at was this:

  1. Remove any export TERM lines from .zshrc, .bashrc, etc.
  2. Set these options in tmux:
set -g default-terminal "screen-256color"
set-option -sa terminal-overrides ",xterm-kitty:RGB"
  1. Kill tmux, close kitty, reopen and true color support should be enabled