Well, without more information, it's hard to say exactly. It could be a visual novel that focuses on the concept of 'broken colors' in a very literal sense. Maybe the characters live in a world where colors are broken or fractured in some way, and the story revolves around how they deal with this strange phenomenon. Or it could be more of an abstract idea, where the broken colors are used more as a symbolic device to convey deeper meanings within the story.
Without having read the novel, it's hard to say exactly. However, it could be a young protagonist who is on a quest of some sort. Maybe there are also some supporting characters like friends or family members who play important roles in the character's development.
Since I don't know the specific '3 colors love story', I can't say for sure who the main characters are. They could be anyone really, perhaps two lovers and a third character who affects their relationship in some way related to the three colors.
I'm not sure specifically who the main characters are without reading it. But they could be people from different parts of the world, representing different cultures and backgrounds.
There could be a villainous character as well. Given the focus on the 'dark', this character might represent all the negative aspects that the title alludes to. They could be manipulative, power - hungry, or just plain evil, causing trouble for the other characters in the story.
It's possible that the main characters are a group of people. One could be a detective - like figure who is investigating a series of events that seem to be linked to this 'evil red'. Another could be a victim who has been affected by the actions of the evil force in the story. And perhaps there is a character who has a special connection to the 'red' aspect, like a person who has a premonition whenever the 'evil red' is about to strike.
Since I don't know the specific 'colors definition graphic novel', I can't say for sure who the main characters are. They could be characters named after colors or characters who have a special connection to different colors.