It's an extended leather thing; the interior leather colour (i.e. not the seats) is continued onto sun visors, roll hoops, etc., but as most go for black interior you don't normally notice it on the hoops.
There's a Z4MR on the AUC website at the moment in Imola with extended Champagne leather, looks a bit weird. It's a combo I favour on other cars, but to me it seems a bit opulent for a hardcore M Car.