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I'm afraid but that I may not of fully understood your question, are you asking if the artwork in the book is sufficient to develop a "official" colour scheme? If so then yes, each model will have original artwork which, despite not covering all sides, should be enough to base a colour scheme off of.
What I mean is for every Hero there is a character sheet with a picture of him available. The picture will show him only from the front ... So you have no backside information how to paint.
And e.g. For the snake... You do not know how the tail with the skull on it looks like in original artwork. See here