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
I dont know about the blue and red coloring and it aint a manga but it sounds similar to https://www.mangago.me/read-manga/a_thousand_cranes/
Watch the interior designers gonna be going out with the brother and the reason he slapped him sgonna be cause their bloodlines gonna end HA
LMFAO