def color_percent(p):
    """Return the adapted color for `p` percent achievement.  `0`
    percent will be dark red, `100` percent will be dark gren. A
    linear interpolation is returned beetween these extrema but a
    coefficient increases the luminosity around the midle `50`.

    TESTS:

    >>> color_percent(0)
    (180, 0, 0)
    >>> color_percent(50)
    (180, 180, 0)
    >>> color_percent(83)
    (41, 200, 0)
    >>> color_percent(100)
    (0, 180, 0)
    """
    coef = 2.0 - (max([p-50, 50-p]) / 50.0)
    # coef = 1
    r = coef*180*(1 - (p/100.0))
    g = coef*180*(p/100.0)
    b = 0
    return (int(r), int(g), int(b))