The Rukh liked to sing, Aladdin realized.
Pretty little harmonies to his ever-present flowing melody were chirped out by the little white butterflies, warm and comforting. The larger Rukh tended to sing lower pitches, steady, base-like hums. Tiny Rukh had more percussive, high-pitched chirps that twinkled like bells. Medium-sized Rukh sang the beat of the tune, a steady harmony the seemed to never stop. It flowed one endlessly, changing keys, changing tune, always.
Different peoples' Rukh had different songs, as well. Alibaba's song was extremely percussive - Rat Tata Tat and Ping Ping Pong - and he went with the beat of his own drum. Morgiana's song was like ballad - constant and smooth and flowing, like a river. Hakuryuu's song reminds him of a funeral march, slow and sad, dripping with grief and loss. Ja'far's song was quick and bouncy, and it reminded him of running - watching the world fly past you through peripheral vision, feeling the wind in your face. Masrur's song was always so quiet, always pianissimo, and low, rhythmic, like a heartbeat. Sinbad's song was insane, and strange to listen to. The notes weren't right, and the rhythms didn't match up, and it sounded like chaos was brewing under the High King's calm outward composure.
Pink Rukh also had a distinct sound, and it was sweet, like sugary, sour candy. The low undertones of the pink Rukh reminded him of long, hot nights, in which he would sweat and wake up exhausted.
The black Rukh, however, didn't like to sing.
Aladdin had heard it, and it made his stomach churn, head ache. The sounds that came of the black Rukh were low, haunting moans, sounds of pain, and hurt and tragedy and it is always so dark and it sound like a enormous, tortured whale that wanted to swallow him up. The smaller Rukh would scream out in agony and anguish, as if they were being beaten and hurt so many times and could no longer bear it.
It was so painful to listen to all that racket by default, but the sounds also seemed to eat away at his heart, at his happiness. The wailing and screeching of the dark Rukh devoured every other sound, until it was silence except for that endless void of tortured noise.
He often wondered how that fallen Magi of Kou could stand to hear all that, every second of every day, and not go completely and utterly insane. Unless he already was, Aladdin thought. He imagined that someone would already have to be hurt so much, to have already suffered past the point of no return, to be able to listen to the haunting sounds of the dark Rukh and be okay with it.
From what Aladdin summed up, he wanted no part in the dark Rukh. He would continue on his melody, and the Rukh his harmony - in an ever-flowing, pleasant song.