There are multiple sides to this issue.

1. we don't draw an overlay for it.
2. the calculation of the colors was in blender 2.79 a per mesh attribute, now it is a 3d view attribute.

The activation of the drawing should trigger the calculation of the colors (draw_cache_mesh).

What colors will be shown is currently a tool setting. also the data is stored in the BMesh (derivedVertColor, derivedFaceColor)
So question is how far will we implement this. eg. should the tool setting become a per view setting (and therefore the data will also be placed there).

Note to self:

• change derivedVertColor and derivedFaceColor to weight. Assign color in shader.