Hi Bruce,
The screen colour is defined in User Preferences, on the Appearance tab. If you don't want users to have any of their own User Preference settings in the 'test data' area, then you can sign into Adagio and the 'test data' as SYS, open User Preferences and set the screen background colour, and finally click the 'Set All Users' button. This pushes all the SYS user preferences to any other user of the 'test' data.
It is conceivable to restore the 'test data' files that store the background colour setting, but that would also copy over all other settings stored in these data files (not just the colours).
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Regards,
Softrak Tech Support