Adwaita GTK2 colors do not match GTK3 theme
The colors of Adwaita GTK2 theme do not match the Colors of the GTK3 theme. GTK3 also has some function which allows background applications to have a different colorset then foreground. This seems not to be implemented in GTK2.
Also full GNOME apps have different colors than regular apps.
Tested with the latest stable released Adwaita version from GTK 3.32.