I noticed some differences with toolbar and notification backgrounds myself (After the upgrade from 4.10 to 4.11). Most notible on my EEEpc. But, I also noticed that the theme on my EEEpc changed from Oxygen to one of the Air themes. Changing it back got rid of the solid black toolbar.
I haven't had time to play with the notification settings yet, but, my guess is that something changed in one of the theme settings.
System Settings --> Workspace Appearance is where I've been experimenting.