def _rv(match):
    """
    Given a regexp match for a color, return the reverse-video version
    of that color.

    @param match: A regular expression match.
    @type match: C{Match}
    @return: The reverse-video color.
    @rtype: C{string}
    """
    str = '#'
    for color in match.groups():
        str += '%02x' % (255-int(color, 16))
    return str