It's been a while since I was involved in painting things like railroad cars and locomotives, but the problem is that the durability of the newer yellows is dependent on what is used as a substitute for yellow chromate. Cost is a factor here. Most likely those substitutes which last better are siginficantly more pricey than those which aren't as durable, and all of them cost more than yellow chromate. Yellow is a component of orange (yellow+red) and green (blue+yellow), so it has affected those colors too. The late Gorge Rust, DuPont's fleet color guy, once told me that he watched a painter at the PRR make Brunswick green by adding a handful of yellow chromate powder to a 5 gallon bucket of lampblack-based paint. Santa Fe olive green can be made by mixing Santa Fe blue with Santa Fe yellow, equal parts of each as I recall, although I didn't get this from him.

> is the orange color on BNSF's Heritage 2 scheme GE's a decal, or is it paint

If it's reflective, then it's a stick-on like Scotchlite, which isn't technically a decal. If not reflective, then it's paint. Reflective stick-ons are quite expensive, so usually it's just the strpes and hearlads which are Scotchlite.

Decals are made using regular paint pigments unless you're making them for glazing patterns on pottery. It also depends on what you think of as a decal, see decalcomania: [en.wikipedia.org]. Dyes are subject to the same ultraviolet degradation problems as pigments, if not more so. Reflective stick-ons mostly use dyes, which have to be transparent enough to let the light pass through to the reflective layer and then back out to the observer. Yellow chromate is quite opague, so I rather doubut it was ever used in applications like Scotchlite. Nothing has yet really matched it in durability and "price efficiency".