Hi David
This should be a simple change in the Theme development/tweaker.
To open the Theme development/tweaker dialoge box, from the pull down menu select Actions > Show action list...
In the filter in the Actions list type "tweak" and it will single out the required action. Double click on that to bring up the Theme developer/tweaker dialogue box.
To change the text colour, near the top, select Window text.
Or, to change the colour of the background select Window background.
Both of these items are very close to the top of the Theme development/tweaker window so no need to set a filter or go searching.
Remember to save the theme from the Theme development/tweaker dialogue box.
cheers
andy