Since there are a lot of flashbacks, have you considered just using the same color as the present tense? Movies like Batman Begins, and Forrest Gump just used the same color all around. If you want to grade and it is a noir film, back and white seems like the best option for noir, but if do not want that, and do not want desaturation, then perhaps different color temperatures. When you shot the feature, did you have an idea of what you wanted the flashbacks to look like originally?