I agree the gray poplar looks much better with a light leather, I went with Gray poplar on my order with Lemon leather for even more contrast. It should look great with the black headliner of the M Sport package too. If all goes as planned, should be picking it up tomorrow and I'll post some pictures
The walnut is nice, but is more suited to sedans like the 5 series or 7. The walnut doesn't match a 135i.