hmmmm...perhaps you have the 'show color on title bar' feature in win10 color settings turned off?
just tested that idea and it had that effect for me as well. To see if that's waht your having open the settings window and go to personalisation > colors and see if "show color on title bar" is turned of. If so try turning it on. I had to open AeroGlassGUI and close it again for the title bar color to be restored after turning it back on.