The purple room in Poe's The Masque of the Red Death represents the second Deadly Sin, which is Greed. Greed, or avarice, is insatiable, excessive desire for wealth and all material goods.
All seven Deadly Sins are, from first to seventh, Pride, Greed, Envy, Wrath (severe anger), Lust, Gluttony, Sloth. Each has a room assigned and each is present in The Masque of the Red Death. The Seven Deadly Sins are of such a monstrous nature because of the other sins that they lead to.
Poe describes the setting as a "voluptuous scene" with seven rooms, "an imperial suite." This indicates that the rooms must be considered together, thus establishing that if the first room represents the first deadly sin Pride, then the second room represents the second deadly sin Greed, and so on. This idea is given support by the fact that the masked ball was held at the end of the sixth month leading into the seventh month.
Since Greed is the sin of having an insatiable appetite for wealth and all luxuries and goods, it leads to other sins against other people, for instance, people who are left without food or shelter. In The Masque of the Red Death, the second room represents the Prince's magnificent preparations for his self-imposed imprisonment with his courtiers.
His country is "half depopulated" yet he is shut up within the abbey's walls with all manner of riches, beauty, wealth, food and wine. The Greed betokened by this insatiable accumulation of food, wine and luxuries leads to the greater sin of his kingdom's people being left to suffer and struggle alone and without necessities.
Additionally, the purple, or second, room represents the stage of life during which humanity is productive and able to acquire the means of sustaining life. This contrasts greatly with the deprivation of others' lives caused by Greed.