looking at that 7.66 instance I see its the window frame background color that is actually what changed. before it was same color as the channel window (white) so it made the window chrome less of a thing vs now. how does one change that?
This is a Windows setting and can be found in the Windows 10 Options, Personalization, Colors section. You may have chosen an accent color along with enabling the "Title bars and windows borders" option.