Well done on getting it all working.
It seems a shame that you've had to resort to an Arduino solution though, when the hardware is already there in the Slice.
It's a great shame that nothing ever came of the Slice "ambilight" option. For a short time it became part of the original Slice Kickstarter campaign, but then the idea was dropped.
I feel sure that had the Ninjas carried on and sold a plug and play solution for this, it could well have been the distinguishing factor that would have made Slice stand out from the crowd of media players.
I still love the idea of ambilight, but I'm resigned to the fact it will never be integrated into Slice. When I'm ready for my next TV, which will be my first 4K, I will definitely look at the high-end Philips models with ambilight.