I like overthinking about main character's signature colors that they mostly wear so let's dig in
Ash- color red. Red is the color of passion, burning fire. Someone who's red coded is described to be hot headed, without much patience. Ash is sometimes seen wearing red jackets or hoodies, but most of the time he wears red converse. Red can also be color of love, and we know Ash doesn't really care if somebody hurts him as long as his loved ones are safe.
He also wears green, a color that isn't excatly the opposite of red but red cancells out green. Green is the color of envy, like how Ash envies Eiji for being able to fly and run away from his problems. Therefore, Ash mostly wears green around Eiji only.
Mostly, he wears a lot of white and I think that's a interesting choice. Someone said it's easy to wash off blood if it's stained on white fabric, but I like to think how Ash is such a dark character with a horrible past and yet, his body features are very light, as well as his clothing choices, where Eiji's the complete opposite, having dark features and his clothing choices that are mostly in darker colors.
Eiji- blue. Blue is the opposite of red, and naturally Eiji is the very opposite of Ash. He's calm, kind and honest. Blue is the color of waves that extinguishe hot fire, just like Eiji's warmness and honesty that made Ash feel safe and complete. But, blue is also the color of sadness, which followed Eiji years after Ash's death.
He also likes pink! Pink is a shade of red, showing he can be as stubborn and obstinate like Ash, but not as much as him. It shows he can be like Ash at some moments, but he still keeps his true personality and doesn't really look up to him, he rather wishes to be on the same page as him even thought that's probably impossible.
And like Ash, he wears a lot of green too. Eiji also envies Ash, for being able to stand up on his feet all by himself when he falls down, while he literally had Ibe drag him to USA to recover from his depression. Besides envy, green is also a color of comfort. Green brings us peace, like watching nature that makes us calm down. Green is also a combination of blue and yellow. Blue is his signature color, and yellow is the color of happiness and innocence (kinda ironic how he represents happiness and depression at the same time)
