Prince Prospero has 7 rooms which could symbolize the 7 deadly sins. This particular room is purple which represents royalty.
The Purple Room
The Dancing Hall
The clock strikes every hour and it makes everyone stop. The people at the party seem freaked out and stare at the clock. The clock could represent the time we have in your life and how we spend it.
The Black Room/ The Masked Man
The prince went into the black room because he was being chased by the masked man. His guests were scared, but didn't want run away. The black room symbolizes death and the red curtains symbolize the blood/red death. The masked man represents the plague.