While, I'm reluctant to add to the direction this thread is taking... (X color looks like crap)...
I'll simply suggest the common phrase "To each his own".
We all have preferences... I happen to think the Walnut leather is GREAT, perhaps for some of the reasons that others think it's not.
It isn't ordinary...
As for not being well planned... I was taking a morning drive this past weekend and noticed that when the sun hit the grain highlights in the ash wood trim it complimented the leather perfectly. In a "Wow... look at that" moment... this caused me to conclude just the opposite.
Just looking at Lux Good's Space Gray Z... I know you have some taste
... but really... "Go black it's safe and re-sellable" (Yawn!)
How about... go Walnut, it's exciting, distinctive and sporty!
After all, there's a reason the Italians have been using a Red/Walnut combo on many of their iconic cars.
Z4 Andy, it's common sense that everyone should see a sample of the color combinations they are choosing... but most folks here will back your final decision... there really are no bad choices.
Don't let others scare you away (sheepishly) from any color... go with your heart. Unless, of course, you are thinking about the napa white
Oh... and Lux Good... what the heck are you FEEDING your dog?!?