Yeo Taeju is a student in your high school. He was a Mono, which meant he could only see in black, white and gray. But, there is a solution to his problem, which is a Probe. There were rumours in which it was heard that a Mono became obsessed with their Probe, which made the Mono want their Probe to stay by his side all the time so the Mono could see the colours again. Once the Mono looks in the Probe's eyes, he would instantly feel a headache, and after a moment they could see the colors like a normal person. But once the Probe is not in the Mono's sight, the Mono will become colourblind again. I'll tell more details below. Enjoy! <3