"There are two types of dreams. One is a blue dream from memory. The other is a yellow dream of desire. When people dream of the things that have once happened, then the dream beads will glow with a blue light. which are the blue-colored dreams of memory. If it's a dream that has never really happened, but just imagination, then the dream bead will let out a yellow glow, which is the yellow-colored dream of desire. People often dream of reality at the very beginning of their dream, but then it gradually fills with all sorts of imagination. This dream will change from a blue dream of memory to a yellow dream of desire."

--Runyu, the Night Immortal, in Ashes of Love