I am running on Lesson4 sample.
As from attached file, the selected faces in fig 1 and fig . 2 are filled with uniform color.
The fig 3 , instead, shows the seletected face non very good. Why does it happen?
Do you render another face on top? It looks like z-fighting (if I'm correctly using this term from rendering world). Try playing with the code in AdjustSelectionStyle() function, e.g., with transparency.