Dinosaurs – Accurate Images Now Available in Color

And we believe this beause...?

Of course, since we weren't there, we can't be 100% certain. But from http://opa.yale.edu/news/article.aspx?id=7249:

"The team closely examined 29 feather samples from the dinosaur and did an exhaustive measurement and location of melanosomes within the feathers. The team then did a statistical analysis of how those melanosomes compared to the types of melanosomes known to create particular colors in living birds, using data compiled by Matt Shawkey and colleagues at the University of Akron. The analysis allowed scientists to discern with 90 percent certainty the colors of individual feathers and, therefore, the colorful patterns of an extinct animal."

Thanks for that, it explains the feather colour. Now what about the skin colour that's being touted? What basis do they have for that?

I'm not sure about that. Everything I read and blogged about was recent as of January and was pretty specific to the feathers. I don't have time now to Google the skin but I imagine there's something out there...

And we believe this because...?

If by this you meant, a connection between pigmentation (of proto feather or feather) and behavior of dinosaur (antecedents of birds), a clear basis for "belief" rests on the analogous connection between coloration (among other displays) and behavior in present-day birds. In particular (but not exclusively), coloration and behavior (responses) acts to help breeding birds become breeding pairs, to the exclusion of non-like species... to inhibit cross species breeding which, more often than not, is unsuccessful (hence, non-survival ...) breeding. The English (as well as US) bird literature give ample documentation .....

When it comes to what strikes closest to the truth of the matter, the growing body of evidence for dinosaur ancestry in birds makes such resort to analogy not unreasonable in determining what makes more or less greater sense for investigators to "believe."

Summarizing, the article of faith rests on scientifically valid conclusion by analogy.