My BOP echo function

function rainbow(a)
    --ColourNote("cyan", "black", a)
    --roygbiv
    rainbow_chunk = string.format("%i", string.len("*** " .. a .. " ***")/7)
    name_holder = "*** " .. a .. " ***"
    rainbow_colour = 1
    while name_holder ~= "" do
        to_echo = string.format("%." .. rainbow_chunk .. "s", name_holder)
        name_holder = string.gsub(name_holder, to_echo, "")
        ColourTell(rainbow_colours[rainbow_colour], "black", to_echo)
        if rainbow_colour < 7 then rainbow_colour = rainbow_colour + 1 end
    end
    Tell("\n")
end

rainbow_colours = {"red", "orange", "yellow", "green", "blue", "indigo", "violet"}