Menubar turns solid white or transparent

Solution 1:

I had this same issue. Using dark mode my screen would appear with the whiteout menu bar on my macbook pro when switched to working in my 2nd monitor. It appears there was a colour profile issue in Settings>Display>Colour Tab. I changed my colour profile to a generic colour on both displays then back to my chosen profile. So far this seems to have fixed the issue.

Solution 2:

I noticed that only 2 of my 4 desktops had the white menu bar; I just deleted those desktops.

Solution 3:

I was able to resolve this by going into Settings > General and toggling "Use dark menu bar and dock" off and back on.

Solution 4:

I had this issue after changing the colour profile of my Macbook and external display from Native to sRGB. Moving back to native or another wider colour gammut profile seemed to resolve the issue for me. Glad I found this as it was really bugging me for weeks.