The blue and purple rooms symbolize birth and youth because those rooms are the closest to the east which represents the beginning because that is the direction from which the suns rises from.
Green represents adolescence since adolescence comes after youth and the green room comes after the purple room. Green also means growth because people in adolescence are still growing and green is the same color of growing plants.
Orange represents adulthood because adulthood comes after adolescence. Orange means that growth has stopped because with plants once they turn orange they have stopped growing.
Black room with a scarlet light
White represents old age because old age comes after adulthood. Because when people get older their hair turns white.
Violet represents imminent death because that comes after old age. Because this is the last room that Prince Prospero passes before he is killed by the Red death in the last room.
Scarlet represents death because that comes after imminent death and the scarlet room is the farthest west which represents the end because that is the direction in which the sun sets. Also the color of blood is scarlet which oozes out of peoples pores when they are infected by the red death.