finally I had some time to spend on GNUe again today and thus I
implemented the long-promised feature to set text and background color
for entries in the form definition.
You can now do:
<entry ... color="RED" background_color="#1A3B4C"/>
It currently only is implemented for the wx backend, and due to some
inconsistencies in WX it does not seem to work for dropdowns. Still, I
hope you find this feature useful.