Are the stock King Hauler frame rails black
 

or do they need to be painted black aftermarket to make the model look like more of the real deal?

I understand they are aluminum.

Is flat black a realist color for truck frame rails and cross-members?

Re: Are the stock King Hauler frame rails black
 

all tamiya's stock rails in the kits are black, i've seen some red and blue optional tamiya ones, but only stock lengths. if you search on the forum or on google images, they come in all colors.

Re: Are the stock King Hauler frame rails black
 

Factory is black.

Aftermarkets are aluminum coloured.

Red/Blue/Greens etc I think are from RC4WD. I have seen them on ebay to. Come blank and you have to drill/tap your own holes.