Change the colour of the fish shell git prompt if source files are newer than build files. Set your prompt to fish_git_prompt then. Add this line to the bottom of ~/.config/fish/functions/fish_prompt.fish

fish_git_prompt_build_status.fish

 #Tests if source files listed are newer than the build

    set currentTime  0

    set rebuild false


    if test -e (pwd)"/"srcList.fish; and test -e (pwd)"/"buildList.fish

        for file in (strings (pwd)"/"srcList.fish)

            if test (stat -c '%Y' $file) -ge $currentTime

                set currentTime (stat -c '%Y' $file) 

            end

        end


        for file in (strings (pwd)"/"buildList.fish)

            if test (stat -c '%Y' $file) -lt $currentTime

               set rebuild true 

            end

        end

    end


    if test $rebuild =  true

        echo -n -s (set_color$fish_color_user) "$USER" $normal @ (set_color $fish_color_host) "$__fish_prompt_hostname" $normal ' ' (set_color $color_cwd) (prompt_pwd) $normal (set_color $fish_color_git) (__fish_git_prompt) $normal $prompt_status "$mode_str" "> "

    else 

        echo -n -s (set_color $fish_color_user) "$USER" $normal @ (set_color $fish_color_host) "$__fish_prompt_hostname" $normal ' ' (set_color $color_cwd) (prompt_pwd) $normal (__fish_git_prompt) $normal $prompt_status "$mode_str" "> "

    end