BackgoundColor doesn't work?

Question

What am I doing wrong here, the BackgroundColor doesn't appear. I tried locally (PlantUML version 1.2024.4) and on the server. This example from 2021 doesn't work now either

Answer 1

Just for the record 
See full exchange about this topic here:

• https://github.com/plantuml/plantuml/issues/1932

Regards,
Th.