The Guardians of the Universe sent Green Lantern Katma Tui to a recently discovered "inhabited world...in the black and lightless void known as the Obsidian Deeps," to appoint a Lantern Corpsman as protector of that space-sector. After much effort, Tui found the world through its gravity field, sparsely populated by bipedal, frog-like silicone-based life forms. Tui's power ring detected a worthy subject amongst the people,and Katma said hello, eliciting an ear-splitting scream. Using her Lantern ring to translate, Katma learned the selected representative's name was Rot Lop Fan, and needed a bit of time to calm him. Flying in as she did, by the light of a small green beam, how was Fan to know anyone was there? Tui attempted to explain her mission, but for the same reason she startled Fan, she was doomed to fail. What does a light source or a color mean to an eternally sightless race?
Time and again, Katma Tui was frustrated by untranslatable words in trying to explain the Green Lantern Corps, but was hampered by the fundamental concepts being lost on Rot Lop Fan. "Stranger? I am sorry that you cannot make me understand you. Though what you say is alien, it has the ring of truth..." Fan's words inspired Katma Tui. "Certainly it's unorthodox, but I'm sure the Guardians will turn a (untranslatable) just this once..."
Katma Tui gave Rot Lop Fan his power ring, and asked him to imagine the shape and weight of a bell. Fan's race was familiar with sonic instruments, and he successfully created a bell with his ring. Tui then explained this bell could "emit sound waves that you can shape into solid forms." Doing so, Fan exclaimed "By the Primal Chime! Will you listen to that!"
Katma Tui learned which pitch Rot Lop Fan found "soothing and restful," then came up with a variation on the Green Lantern Oath he could understand...
In loudest din or hush profound
My ears catch evil's slightest sound
Let those who toll out evil's knell
Beware my power:
The F-Sharp Bell!
Green Lantern Katma Tui gave F-Sharp Bell Rot Lop Fan a modified uniform, and didn't bother about the ring's vulnerability to the color yellow, for obvious reasons. She then had to return to Oa and explain to the Guardians of the Universe that while they had gained a new Corpsman, he was not a Green Lantern. The Guardians understood the cause for Rot Lop Fan's uncertain status as a Green Lantern Corpsman, and promised not to keep him in the dark for long. Later, while taking in some R&R, Katma realized that was the first time in her years of service she'd heard a Guardian make a joke. "She felt vaguely uneasy for the rest of that day."
"In Blackest Night" was by Alan Moore, Bill Willingham & Terry Austin. It was one of the first GLC stories I ever read, and a favorite.