I'm actually looking at those too! But in Flat Black.
I think the white would be great but hard to clean.
Gunmetal would be different and i think it would go GREAT with NBP. You see too many NBPs go with silver or black... so why not in between
+1 gunmetal
p.s.- i don't know if you've considered this, but bronze and gold go very nicely with NBP as well