Sets the color for this data set.
        
        :param      color | <QColor>

def setColor(self, color, key=None):
        """
        Sets the color for this data set.
        
        :param      color | <QColor>
        """
        self._color = QColor(color)
        if key is not None:
            self._colorMap[nativestring(key)] = self._color