Some possible alternatives...
try switching the orientation of some of your neapolitan blocks so that all the vertical ones are facing the same way
try alternating the pinwheels with the neapolitan blocks in the border.
try using the dark brown instead of the pink in the pinwheels...ie have some darker brown and some lighter brown
Don't know how any of these will actually look...might not be any improvement at all...as you said, idea looked great on paper...these look good in my head!