I understand this phrase to mean that something is beyond dispute, in other words a starting point for the discussion:
“I think it’s taken as red that we are going to open an office in Texas, the question is whether we are going to do it in the Spring, or wait till next year.”
A friend of mine, who is generally trustworthy about this sort of thing, says that this phrase comes from New Testament Bible study. In the Gospels, the quotations from Jesus were printed in red ink so they would stand out. Thus “taken as red” meant “the Word of God,” and thus beyond dispute.
I’ve heard the phrase spoken far more times than I’ve seen it written down, but I always assumed that it was “taken as read” as in, “we’ve read that already, and everyone is on the same page, now what?”