I had the same problem - just changed the settings and couldn’t change them back to get the colours back.
The problem is with the file users//AppData/Roaming/Steinberg/Wavelab/Presets/LevelMeter/previous.last (Windows).
There may be an easier way, but I reset the prefernces by renaming the Wavelab folder in AppData/Roaming/Steinberg, running the program to create new preferences, then copying the new LevelMeter/previous.last file into the old prefs and then renaming this folder and removing the new one.
I hope this helps…