Colored bash prompt and tab title

Question

I cannot seem to get both a colored terminal prompt and the tab title to change at the same time.

function tab_title() {
    local tab_replace="${USER}@${HOSTNAME}"
    local tab_orig="$PS1"
    local tab_new="\e]2;${tab_replace}\a"
    echo "${tab_orig}${tab_new}"
}

function colour_prompt() {
    local c_off="\[\033[0m\]" # Colour off
    local c_red="\[\033[1;31m\]" # Colour red
    echo "${debian_chroot:+($debian_chroot)}${c_red}\u@\h${c_off}/"
}

PS1="${tab_title}${color_prompt}"

I never managed to get the alternative tab title working

echo -en "\033]0;New terminal title\a"

What am I doing wrong?

Also, what are the $debian_chroot variables for?