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Description
When you make 2 2dhistograms, and go in Style/Traces/By Type, you don't see any Points: marker.color (MarkerColor) controls.
When you make 2 2dhist + 2 scatters, you see points.marker.color controls appearing.
Plotly.Plotschema.get().traces.histogram2d.attributes, shows that marker.color is a possible attribute on 2d histograms, but that control only shows up in the grouped tab. And only when grouped scatters are made along with histogram 2ds.
Discovered during: #611