Determines the target color type from the vector y as follows:

            - if y is None: only a single color is used
            - if target is auto: determine if y is continuous or discrete
            - otherwise specify supplied target type

        This property will be used to compute the colors for each point.

def _determine_target_color_type(self, y):
        """
        Determines the target color type from the vector y as follows:

            - if y is None: only a single color is used
            - if target is auto: determine if y is continuous or discrete
            - otherwise specify supplied target type

        This property will be used to compute the colors for each point.
        """
        if y is None:
            self._target_color_type = SINGLE
        elif self.target == "auto":
            # NOTE: See #73 for a generalization to use when implemented
            if len(np.unique(y)) < 10:
                self._target_color_type = DISCRETE
            else:
                self._target_color_type = CONTINUOUS
        else:
            self._target_color_type = self.target

        if self._target_color_type not in {SINGLE, DISCRETE, CONTINUOUS}:
            raise YellowbrickValueError((
                "could not determine target color type "
                "from target='{}' to '{}'"
            ).format(self.target, self._target_color_type))