I switched the windows theme to high contrast (white on black) and back to windows default (white/blue) and the background for the properties/layers toolbars are stuck as black.
I have gone into File/Properties/Rhino Options/Appearance/Colors and changed it back to default and it fixes it until I click OK.
OK so yet it worked indirectly, the reg listed below had a value of 0, i deleted it, reopened rhino, but didn’t work.
So then i changed it to a different value 13160660 (the ugly grey), then opened rhino again and it was the ugly grey. yay.
Then i deleted the reg again, reopened rhino and its back to white/grey.
But, Rhino seams to have a bug that has to be fixed. In my case I switched the Windows Theme from an Aero theme to “Windows Classic”, started Rhino, closed Rhino and switched back to the previous Aero theme, which left a dark grey tab background. Rhino seams to store the color in the registry but offers no possibility to change it. It would be nice if the bug will be fixed. Don’t know how to trigger the developers.