Thanks for sharing this!
This is looks like another shading option. And I think this color should come from a theme setting
To solve the first issue and get this new overlay color the theme tree should look something like:
3D View
– Face Solid*
– Face Wire
– Face Retopology
– Face Selected
– Face Dot Selected
*current Face
And could Face Retopology share the Face Wire color? Something like Face Overlay? I’m not sure about the different use-cases here.
The second issue could be related to the drawing order. I’ll have to investigate further.