I can't prove it but still think 340s roof was painted red for the Elks club special.
The only part of 340s roof we know is metal is the curved hatch cover. Who knows what the rest of the roof is covered with. It could be metal, could be canvas, or felt paper and tar.
I will say this, 340s roof was red in the early days at Knott's.
Now for the topic at hand. It has been said canvas and tin was an early option for cab roofs same for cabooses. To that end lats take an excerpt from the 1904 lettering diagram for cabooses. "When caboose has tin roof, roof to be painted with Princes mineral brown." This was practical to help protect the tin but would have also been a style choice. I have no idea(Or can't remember) if this would have been the same practice for locomotives but, it is Definity a possibility.
I don't think it was coincidence that Knott's chose to paint the roof red on 340, the same color we are arguing about from a photo before she went to Knott's.
Jeff Taylor
CRRM curator of equipment and rolling stock.