Light: The words that come to my head with red are deception and hatred. Light obviously has lied to countless people, and he has a general hatred of the world. This is why I believe this color was chosen for him.
L: The color blue makes me feel calm and peaceful. L deals with very serious matters all the time, but he does it in a way that calms everyone around him. He is very quiet and calm, only speaking when he needs to.
Misa: A word that light blue brings to my head is innocence. Misa is an extremely innocent person, and that is why she got into the mess with Light. She developed an obsession for a guy and took it too far without thinking of the consequences.
Matsuda: The color yellow makes me feel positive and happy. Matsuda was the comedic relief character so this one is quite self explanatory. He never failed to make me smile, even in the most tense scenes.
Yotsuba Group: When I think of purple, I think of a sense of superiority, thinking that you’re better than everyone else. The Yotsuba Group believes that they are superior over everyone, and I believe purple was chosen for them because of this.
Aizawa: Dark green makes me feel murky and depressed. At the beginning of the show, I would describe Aizawa as a light green. Pretty optimistic and positive. However, as the show progresses, his shade of green gets darker and dark, showing off his true color.
Mikami: Same with the Yotsuba group. A sense of superiority over others (except Kira).
N: The color white feels very pure. N has almost no experiences with real life and devoted his life to solving crime at a young age. Because of this, the color white matches him perfectly.
Sorry you had to read my essay of thoughts lol