Shutter Island opening scene analysis

During the opening scene of Shutter Island, the scene switches between flashbacks and reality. This is shown through colour; colour during reality is less vibrant and darker whereas during the flashbacks the colours are more vibrant and 'happy' colours like green and yellow. This shows that the character's flashbacks take him back to a time when he was happy. This creates an enigma as the audience wants to know what happened to him.