code: def test_op_ndoverlay_value(self):
      colors = ["blue", "red"]
      overlay = NdOverlay(
          {
              color: Bars(np.arange(i + 2))
              for i, color in enumerate(colors)
          },
          "Color",
      ).opts("Bars", fill_color="Color")
      plot = bokeh_renderer.get_plot(overlay)
      for subplot, color in zip(plot.subplots.values(), colors):
          self.assertEqual(subplot.handles["glyph"].fill_color, color)
  
imports: import numpy
  from bokeh.models import CategoricalColorMapper, LinearAxis, LinearColorMapper
  from holoviews.core.overlay import NdOverlay, Overlay
  from holoviews.element import Bars
  from holoviews.plotting.bokeh.util import property_to_dict
  from ..utils import ParamLogStream
  from .test_plot import TestBokehPlot, bokeh_renderer
label_desc: Use image node_id 28 for calling the TestBarPlot obj's underlying member method code with example usage: obj.test_op_ndoverlay_value() without return types