Earlier this week, Nokia France made a statement that "new colors for the Lumia 800 are under consideration" while an interview with monwindowsphone. The estimated time for these colors to be available in the market is Q1 2012. The availability of these Colors will depend on the costumer demand and Nokia's estimated Sales Volume.
You can easily see Lumia 800 in two new colors, Yellow & White. However these colors are not finalised and depend upon the factors stated above.
