    def _change_colours(self, colour, attr, bg):
        """
        Change current colour if required.

        :param colour: New colour to use.
        :param attr: New attributes to use.
        :param bg: New background colour to use.
        """
Change current colour if required.

:param colour: New colour to use.
:param attr: New attributes to use.
:param bg: New background colour to use.
asciimatics/screen.py