URGHH... sorry, but have just taken a look into their forum source code, found among other sources an adservice at nuggad.net and opened that site directly. There's an advert for "smart audience universe". Click on that thumbnail - it just makes you SICK to the stomach again!!!
They praise how detailed they can deliver you ads:
not just by interests, but also by hundred other details, like
Children in household
Head of household
Main income earner
PLANNING TO MOVE:
to a flat
Intent on buying a car within the next 12 months
and LOTS more
As to your question, it's not as easy, because Mozilla exceptions work only by domain and prefixes, as far as I know.
But with some investigation inside the source code there are probably some tricks. Also because nowadays lots of sources are from foreign domains, like the one above. For starters you can try to block that nuggad net domain (which will then work on the whole web, not just here).
Or if you find inside the source code special "class" entries for the colors you need, there may be a chance to inject a little custom style mimicking those.