added RGB 24-bit colour support automatic detection

.tmux.conf

@@ -712,9 +712,21 @@ run 'cut -c3- ~/.tmux.conf | sh -s _apply_configuration'
 # }
 #
 # _apply_overrides() {
-#   tmux_conf_theme_24b_colour=${tmux_conf_theme_24b_colour:-false}
+#   tmux_conf_theme_24b_colour=${tmux_conf_theme_24b_colour:-auto}
 #   tmux_conf_24b_colour=${tmux_conf_24b_colour:-$tmux_conf_theme_24b_colour}
-#   if _is_enabled "$tmux_conf_24b_colour"; then
+#   if [ x"$tmux_conf_24b_colour" = x"auto" ]; then
+#     case "$COLORTERM" in
+#       truecolor|24bit)
+#         apply_overrides=true
+#         ;;
+#     esac
+#     if [ x"$apply_overrides" = x"" ] && [ x"$(tput colors)" = x"16777216" ]; then
+#       apply_overrides=true
+#     fi
+#   elif _is_enabled "$tmux_conf_24b_colour"; then
+#     apply_overrides=true
+#   fi
+#   if [ x"$apply_overrides" = x"true" ]; then
 #     case "$TERM" in
 #       screen-*|tmux-*)
 #         ;;

.tmux.conf.local

@@ -42,8 +42,13 @@ tmux_conf_new_session_prompt=false
 
 # RGB 24-bit colour support (tmux >= 2.2), possible values are:
 #  - true
-#  - false (default)
-tmux_conf_24b_colour=false
+#  - false
+#  - auto (default)
+#
+# automatic detection relies on the COLORTERM environment variable being defined
+# to 'truecolor' or '24bit' or '$ tput colors' answering '16777216'
+# see https://github.com/termstandard/colors
+tmux_conf_24b_colour=auto
 
 # default theme
 tmux_conf_theme_colour_1="#080808"    # dark gray