This change of colour is due to the presence of major quantity of suspension particles in the least blue side and less concentration in the blue side. It can be because in this point the wave "feels bottom" (depth is sallower than L/2 where L is the wave length) and suspend the sediment, or because a current exists with contribution of sediments that come from another erosion zone. http://mgg.rsmas.miami.edu/groups/msc101/presentations/Ocean%20Waves.pdf