The Masque of the Red Death, although not strictly allegory may be more metaphor: We will all die. You cannot escape death. You may remember from history, the "Black Death" (yes, the body turned black), the plague, colera and other hard to control diseases. Think of the "Red Death" in this way.
So, the prince has a masked dance, and in walks the uninvited guest, "The Red Death". I'm not sure you mean paradox so much as irony, since red is the color of blood, which we need to live, and red here is the color of death. When this dancer comes in he leads the guests to their inexcapable death. There really isn't a heavy plot the way we think of it, and the setting of the dance is appropo for that time. The wealthy, like the Prince would often excape to a country home until the epidemic ended. This prince thought he would be safe, but alas, he was not.