def chroma_correlate(s, Y_b, Y_w, Q, Q_w):
    """
    Returns the *chroma* correlate :math:`C_94`.

    Parameters
    ----------
    s : numeric
        *Saturation* correlate :math:`s`.
    Y_b : numeric
         Tristimulus values :math:`Y_b` the background.
    Y_w : numeric
         Tristimulus values :math:`Y_b` the reference white.
    Q : numeric
        *Brightness* correlate :math:`Q` of the stimulus.
    Q_w : numeric
        *Brightness* correlate :math:`Q` of the reference white.

    Returns
    -------
    numeric
        *Chroma* correlate :math:`C_94`.

    Examples
    --------
    >>> s = 0.0199093206929
    >>> Y_b = 100.0
    >>> Y_w = 100.0
    >>> Q = 22.209765491265024
    >>> Q_w = 40.518065821226081
    >>> chroma_correlate(s, Y_b, Y_w, Q, Q_w)  # doctest: +ELLIPSIS
    0.1210508...
    """

    C_94 = (2.44 * (s ** 0.69) *
            ((Q / Q_w) ** (Y_b / Y_w)) *
            (1.64 - 0.29 ** (Y_b / Y_w)))

    return C_94