Convert a hex color to a special sequence.

def set_special(index, color, iterm_name="h", alpha=100):
    """Convert a hex color to a special sequence."""
    if OS == "Darwin" and iterm_name:
        return "\033]P%s%s\033\\" % (iterm_name, color.strip("#"))

    if index in [11, 708] and alpha != "100":
        return "\033]%s;[%s]%s\033\\" % (index, alpha, color)

    return "\033]%s;%s\033\\" % (index, color)