Responses
I dont know about the blue and red coloring and it aint a manga but it sounds similar to https://www.mangago.zone/read-manga/a_thousand_cranes/
It unfortunately isnt but i appreciate ur help <3
Im once again trying to find this manga. It was dark because the MC ran away from his (SA) abusive home. A yakuza guy helps him out and they develop a relationship. All the while the MC is trying to get his little sister out of the household. Some action but there would be panels where the artist would play around with blue and red coloring