Setting up truecolor (24 bit color) in emacs in the terminal, under iTerm2

colorize-emacs.bashsource

# sourcing this file will define a bash functions that 
# tries to run subsequent calls to emacs with 24 bit color.
#
# It sets TERM to xterm-24bit if we're running in iTerm2
# and we've created a user-local terminfo record for xterm-24bit
#
# This will cause emacs to use 24 bit color only when it will work,
# inside or outside of tmux
#
# details: https://gist.github.com/XVilka/8346728
emacs () {
    if [ "$LC_TERMINAL" == "iTerm2" -a -f "$HOME/.terminfo/x/xterm-24bit" ]
    then
        TERM=xterm-24bit command emacs "$@"
    else
        command emacs "$@"
    fi
}

install-terminfo-xterm-24bit.bash

#!/bin/bash

# adds a terminfo entry defining a new terminal xterm-24bit
# If you run emacs (26.1+) setting TERM=xterm-24bit, then it
# will use 24bit color
#
# after running this, you can use colorize-emacs.bashsource to enable 24bit color


cd $(mktemp -d)
cat <<EOF > terminfo-24bit.src
# Use colon separators.
xterm-24bit|xterm with 24-bit direct color mode,
  use=xterm-256color,
  setb24=\E[48:2:%p1%{65536}%/%d:%p1%{256}%/%{255}%&%d:%p1%{255}%&%dm,
  setf24=\E[38:2:%p1%{65536}%/%d:%p1%{256}%/%{255}%&%d:%p1%{255}%&%dm,
# Use semicolon separators.
xterm-24bits|xterm with 24-bit direct color mode,
  use=xterm-256color,
  setb24=\E[48;2;%p1%{65536}%/%d;%p1%{256}%/%{255}%&%d;%p1%{255}%&%dm,
  setf24=\E[38;2;%p1%{65536}%/%d;%p1%{256}%/%{255}%&%d;%p1%{255}%&%dm,
EOF

tic -x -o ~/.terminfo terminfo-24bit.src
rm terminfo-24bit.src