Menubar turns solid white or transparent I have an interesting problem for quite some time now. My menubar turns all sorts of states on external monitors.

I have a 3-monitor-setup on an iMac 5K. I use two external Dell displays to the left and right of the built-in screen. On my right display, when it is inactive, the menubar turns completely transparent, except for the status icons. On my left display, everything stays normal, whether active or not. On my main display the menubar turns opaque white (including status icons) when inactive.

Here's a screenshot of the situation on the main monitor: 

And here it is on the right-most-display (icons blurred for privacy): 

Several reboots and even a macOS update (it happened on 10.13.0, too) didn't fix it, neither did manually killing SystemUIServer. What can I do?

Installed tweaks affecting the menubar (no difference when disabling): Bartender, BetterTouchTool

OS: macOS High Sierra 10.3.1 (17B1003)
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.