I have noticed that some railroads, the logos do indeed change to some degree. This is nothing new of course, like how on the front of some engines things get added. Particularly like the Pennsylvania Railroad having the Keystone with maybe golden accents on it, or the New York Central adding "System" on it.
My main question becomes on color. I have noticed that some logos have a color change on the, again with the New York Central blues or reds. I'm curious how many color changes on the logos there are, mainly the New York Central as I have seen I think a gray logo on a model. Is this correct for a certain time period or a good?
Any other logos of other railroads I'd also like to know about, as you can never learn enough.