Another thing worth noteing is then, as now, metaphors, allusions, kennings and poetry may be employed for a powerful emotional and symbolic effect. You cannot assume everything was intended literally, especially when browsing snippets of colour descriptions from a range of ancient texts, and quoting them outside of their original and intended context.
http://archaeologynewsnetwork.blogspot.be/2014/02/were-ancient-greeks-and-romans-colour.html