Doug,
You wouldn’t have a comma here after ‘blush’, because blushing doesn’t involve speaking – it’s a matter of meaning here, not punctuation. What you have is two distinct unconnected sentences (1: he blushed. 2: his quoted speech).
If you’d said ‘He shouted, “It’s just a metaphorical…”’ then you should use the comma.
In fact, that’s not strictly true…
Using a comma after the dialogue tag is the default, but you can equally use a colon or no comma at all, depending on the context and the effect you’re after.
E.g. With a very simple phrase (He said “Yes!”) a comma can look a little fussy and some writers omit it. That’s fine: it’s a matter of style.
With quotations which are long/complex (especially if they’re made up of more than one sentence) or if you want to emphasise it, you can use a semi-colon.
He screamed: “It’s just a metaphorical ejaculation, not for real. But I can see how you might be confused if we were just text on a page, instead of real-life, flesh-and-blood human beings just talking.”
Again, both the comma and the colon are correct here.
But… dialogue tags afterwards are a bit more complicated, because American English and British English treats them slightly differently. Putting it simply, Americans lob all the punctuation inside the quotation marks, whether it makes any sense or not, and irrespective of the punctuation of the original sentence. The British practice is to try to reflect the original punctuation as much as possible. I.e. if the original is a complete sentence OR it has a comma, we put the comma inside the quotation mark. If it’s not a full sentence and there’s no comma there, we put it outside the quotation mark.
Original: Go home, and never come back. (Original has a comma.)
American and British: 'Go home,’ he said, ‘and never come back.’ (…so even the British put the comma inside…)
Original sentence: Go home to your father. (I.e. no internal punctuation.)
American: 'Go home,’ he said, ‘to your father.’. (Never mind the sense, lob the comma inside…)
British: 'Go home’, he said, ‘to your father.’ (The original didn’t have one, so the comma goes outside…)
That’s the classic explanation anyway (it’s taken from the Oxford Guide to Style). No doubt we’ll move the American way in time — may already have done so…
I don’t know which version Canadians use, I’m sorry…