The Xt is just available in the one colour option, the shifters are 30% ligther action with 20& less movement to get your gear a bit like XTR.
The side swing front mech is awsweome gives real positive shift and more clearance on the gears so less chain rub on extremes.
42 Cassette is only for the 1 ring setup this was due to the chain length i believe being to long and creating too much slap. (no one likes it slapping about)
Rear mech has external adjuster now for the clutch spring.
The side swing mechs are also designed to work with specific chainsets the pickups are in a different place to normal.
Brakes are pretty much unchanged just a slightly different bite point to previous models.
When you ride it is very light weight shift and feels really positive this will definitely be a big groupset for Shimano and will set the bench mark.