Research and Planning - A comment on lighting, Dexter

I have recently watched the entire series three of a crime TV show called Dexter and although we are working on movie trailers and not TV shows this ending scene in episode 11 made me realise how much lighting can effect the mood of the scene, now me and my girlfriend where discussing why this drain of colour was so brilliant at setting a mood and we came to a few conclusions.

Could it be showing how killing someone close is draining the life from Dexter, or maybe how he is cold and emotionless or even contemplating his actions and regretting what he did. Either way I believe this to be an emotive lighting technique for any dramatic scene and made me realise the importance and how I could use it in my trailer to tell a lot about the genre of the movie without making it to obvious.