It seems like the theme dark mode only affects binder, editor and a few others. The toolbar and format bar are the same colour as in the default mode, a very light grey. The same seems true for the theme grey matter dark.
Addition: The dialogs are also very pale grey in dark mode. However, the size of the dialogs is much better now!
Addition: an image to illustrate the issue.
The toolbar text stays white so we can’t see the any menu box unless we hover.
All the windows are also with the white theme (example with compile windows, but it’s the same thing for all the pop up windows)
I can confirm that this is happening to me as well. I’m rolling back to RC6.
Same for me with Hidpi RC7 on Window 10 (1909). Rolling back to Hidpi RC6 corrects the issue.
Same issue for me, RC7 HiDPI
Same issue for me, RC7 HiDPI. I have found that it affects all custom theme color modes except the default. Also, the menu items are missing. They appear if you mouse over them.
This has been fixed and will be available in the next update.
Will this be before June 30th? That’s when RC6 ends.
Fixed RC7 and available in RC8 is the way I read it.
Just downloaded and reinstalled… RC7 hi-dpi is not fixed ATM.
I am experiencing the same issue in RC7’s high-dpi version. Screenshot: 
Sorry for any confusion, I was not very clear in how I explained that. They say that they have fixed their internal copy of 7 and the fix will be available to the public (us) in RC8.
That makes sense. Thanks!