I made ages ago some playlists based on genres, not as how the system tells them, but how I feel them. One of the genres was "white". So music I thought feels white (as opposed to black, green, red etc). I ended up making a playlist for that, and just dragged everything I thought fits that category in it. (I hate the default genres, so I hide them)
So if it's just an internal rating system that the existing labels, genres etc can't do, either just do rating as ElDiablo suggested, or just make separate playlists and drag manually (assuming there is no common denominator for the individual pieces in one category or color).