ok,i might agree,and if gun metal with red stripe?no? somehow i am afraid of one colour wheels!
the another question what is the code of real gun metal? 
You might agree?

You could also paint 2 pairs of wheels. The 2 of the left in Gunmettal , the 2 right ones black with a red stripe.
P.s. I don;t know the color code , but you're local painter does.