docs: def set_gridcolor(self, color):
          """set color for grid"""
          self.gridcolor = color
          for ax in self.canvas.figure.get_axes():
              for i in ax.get_xgridlines()+ax.get_ygridlines():
                  i.set_color(color)
                  i.set_zorder(-1)
          if callable(self.theme_color_callback):
              self.theme_color_callback(color, 'grid')