On mine the channels have signs of being painted body colour. Not very much left though, pretty well all peeled off and now just chrome. IMO they look best just chrome.
Indeed, I just now discovered that they are supposed to be body colour, and they are still intact on my unrestored 1956.. (the poor little bugger on the pics was found dead near the base of the radiator.. probably after eating too much seat foam inside the car).
'64 Parisienne CS "barn find" - last on the road in '86 ... Owner Protection Plan booklet, original paint, original near-mint aqua interior, original aqua GM floor mats, original 283, factory posi, and original rust.
!956 were painted body colour but 1955 Laurentian and Pathfinder Deluxe were painted black. My 55 Pathfinder station wagon that looked to be original paint when I bought it the hood mouldings were painted the body colour Navajo Tan. A parts car I purchased a 55 Pathfinder station wagon were painted the body colour of green. I doubt if anyone went to the trouble to paint them the body colour and they look to be factory but the green ones have lost 95% of the paint.