The black trim is actually one of the reasons I chose a white Model X. It creates a nice contrast (along with the black roofline) and breaks up the massive amount of sheet metal! With everything in black it looks like one huge blob, but would look even worse on a white car IF it was all colour-coded white like you often used to see with 1980s hot hatches!
Interestingly Jaguar have gone for a different solution with black stripes down the sides to break up the slab and create an illusion of a coke-bottle waist. That's perhaps a more elegant solution, but a little contrived, and I do like having sacrificial plastic around the wheel arch edges to avoid chips and scuffs.