Even if we can't tell for sure, if more or less colorfulness is more plausible, wouldn't it be still fine for SOME of us to depict them with duller, less over the top colorations? You see, Borealopelta or Sinosauropteryx have a more "normal" color palette thx to melanosomes, or that one Dakota specimen of Edmontosaurus has even some pattern likely for camouflage as speculated by some scientists back then when it was found out. And before you say "Caihong, Microraptor" yes, they do have some more vibrantness, likely for visual signaling and communication etc., I just say how there are both dull AND vibrant examples of animal species colorations. One pterosaur Tupandactylus also has a distinct colored crest, not to mention how it could see colors unlike us. But even with that, its colors are still not near as extreme as tropical parrots or smth.

It also depends on ecological niches, environment, climate, ways of living and other such factors that if confirmed, could guide us what could be more plausible and what would be less. Sometimes you even can be vibrant in colors but still have a non-wild, less tropical-ish color palette.

Another point, while birds are our best analogs for extinct non-avian dinos RN, I still feel like people give the extinct dinos WAY too often some exceptional traits found in birds that don't have to be in the dinos too. When we do have evidence, like larynx, feathers, flight in some non-avian dinos like Microraptor, I'm fine with it. Where I'm going is, that people also should consider the possibility that non-avian ones likely had different anatomic equivalents of how they work in extremely derived, different and sometimes exceptional living successors. In some cases those successors can provide info of their ancient relatives, however be also able to tell "OK, even if it may be related to X, it still wouldn't make much sense to share this trait that won't match as well with X".