I well remember the "blackbonnet" catalog from those earlier years because when I saw that catalog depiction way back then I immediately knew that I wanted it. I never received it, of course, because it was never produced at the time.
I tend to give far more credence to the account of artist error resulting from the lighting making the prototype image he worked from appear black. I would tend to discount the report of it being a printing error because that would not account for silver appearing as silver on the tank car that came with that set and which is depicted in the same piece of catalog art. Anyone familiar with printing processes would know that such an error would not likely result from a problem in the process.
Many years later--just a few years ago, to be more precise--I bought all four Warbonnet paint schemes (red, yellow, blue, and black) on models produced by Williams. Still have all four, and all are still new in box because I'm waiting to get a wall case so I can display all four in my home. I still consider the F3 in Santa Fe Warbonnet scheme, no matter what the colors, to be among the most attractive locomotives ever to ride the rails.