I ask because it's colored exactly the same as the End Round which I know is not played.
So do you place the portcullises as the ONLY event in Round 5 then move immediately to Round 6?
No, you play the full round. The color does not mean "don't play" it just means "something special happens" In this case, that "something special" is dropping the gates. At the end of the game it just means game over.