First: a question about Shapeway. Who they are and what they can do for someone who wants to scratchbuilt a building for their layout?
Second: a comment about the white painted lettering I saw in a photo of an NW2 B&O switch engine.
Based on my knowledge of yellow pigments, I suspect the yellow lettering contained some lead chromate; this was one of the most common ingredients in yellow paints for outdoor and long lasting uses. I do not think it would fade to white no matter how long it was exposed to the sun light.