1. Symbolism
The clock represents the time that the people locked in Prospero's sanctum.  Every time the clock tones, people realize that their time left to live is growing shorter.  The clock in a sense represents their mortality and the limit that is placed on it.

The name Prospero represents the prosperity that this man tries to create for himself, and how it contradicts the immediate death and destruction that is occurring outside of his isolated existence.

East and west in the story symbolize the rising and setting of the sun.  As the story progressed, the party goers gradually moved form the east where they began to the west where they were killed by the Red Death.

The abbey in the story represents the immorality and sin that Prospero and his group commit while locked inside.  An abbey is generally a secluded building where monks can live sin-free lives and worship, while Prospero uses an abbey for the exact opposite purpose.

The room colors in the story are blue, purple, green, orange, white, violet, and black.  Blue represents deity, eternity, and innocence; purple represents authority, royalty, sensuality, and decadence; green represents hope, growth, life, and future; orange represents warmth, wealth, and eroticism; white represents joy, feast, truth, purity, winter, and old age; violet represents cheerful, exciting, and shocking; and black represents darkness, deepest mourning, deviation, and sin.  Each of the rooms represents one of the seven deadly sins, blue being the least sinful and black being the most.

2. Irony
The irony in the fact that Prospero locks himself in an abbey is that traditionally abbeys were a place of worship and solitude for monks, and Prospero locks himself in the abbey to commit sins and indulge himself in worldly pleasures.

It is ironic that the narrator describes Prospero as "happy and dauntless and sagacious" because Prospero is in fact the opposite of all those things.  He constantly sought to become happy by surrounding himself with worldly pleasures, although he was not by himself a happy person.  He was not dauntless because he was in the first place intimidated by the red death and the destruction it was causing, so he locked himself away and tried to run from the problem.  He was never sagacious in the story because he fool heartedly attacked the red death and caused his own destruction by locking himself away.

The name Prospero is ironic because he was never prosperous.  The closest thing to prosperity he ever attained was destroyed after the Red Death killed him and destroyed everybody that was attending his false paradise.

3. Characterization
Prospero's friends were described in the story as "a thousand hale and light-hearted friends from among the knights and dames of his court..."  These people were the fortunate and wealthy people that were thus far spared from the Red Death by isolating themselves from the common peasant folk.  As the people they ruled over were suffering terrible and gruesome deaths, they lived a luxurious and burden free life; indulging in pleasures and sin.  In the end, they suffered the same fate as the people they were trying to avoid.