def _hue2rgb(v1, v2, vH):
    """Private helper function (Do not call directly)

    :param vH: rotation around the chromatic circle (between 0..1)

    """
    while vH < 0:
        vH += 1
    while vH > 1:
        vH -= 1
    if 6 * vH < 1:
        return v1 + (v2 - v1) * 6 * vH
    if 2 * vH < 1:
        return v2
    if 3 * vH < 2:
        return v1 + (v2 - v1) * (2.0 / 3 - vH) * 6
    return v1
