The silver RiRi zips definitely look amazing on the flash dual zip ups. But I get what you're saying about the black zips with charcoal. I do think they choose not to use black on those because you constantly zip and unzip those zips, and it would fade/chip/discolor real fast..and look bad.
The matte black riri zips actually hold up really well. I've had my
loop wheel black dual flash since it dropped and use it a lot and no chipping/discoloration thus far.