"That at the eastern extremity was hung, for example, in blue..."
See in text (The Masque of the Red Death)
The rooms are ordered from east to west, matching the sun's path across the sky, beginning with blue and ending with black. The course of a day is a common metaphor for the transience of life. The color blue, associated with the sky, can represent vitality and the start of a new day. Black is commonly associated with death and night. The ordering of the rooms can be read as a metaphor for the stages of life, with blue representing birth and black representing death.