1.) Colors can often symbolize feelings. For example red can be envy, anger, vengeance, love. Grey could be gloomy, depressed, nostalgic, sad, tired. Yellow could be bright, cherry, optimistic, enthusiastic.
2.) you could say: to see how the same characters might react to various experiences. Or because it would be cool to read about how when you change one aspect of the story, the rest of the storyline gets molded around that change. For example the setting alone can alter the course of the story.