Converts color strings into a color listing.

def colors(self, value):
        """
        Converts color strings into a color listing.
        """
        if isinstance(value, str):
            # Must import here to avoid recursive import
            from .palettes import PALETTES

            if value not in PALETTES:
                raise YellowbrickValueError(
                    "'{}' is not a registered color palette".format(value)
                )
            self._colors = copy(PALETTES[value])
        elif isinstance(value, list):
            self._colors = value
        else:
            self._colors = list(value)