It's been written that the army did not use the Transportation Corps logo til well after WWII.
Agreed.
What is the origin of the original image of the caboose of the OP?
Fantasy.
If you want to use the word fantasy in that context then everything we run and run on in this 3 rail O gauge hobby is fantasy. We run on fantasy 3 rail track with engines with little electric motors, horn, whistle, bell and other sounds from an electronic circuit board, cars and scenery with little fantasy plastic or metal figures and the list goes on. It's called "fun" and it is diversified over all whole hobby.
I would love to have a model of this caboose on my new Army layout.
Steve and Lady
But, the question was if the paint schemes used on the RMT and Weaver models shown in the OP. Are they fantasy or not?
There has yet to be conclusive proof presented that they are not fantasy, save for some decidedly European examples.
An individuals preferences for fantasy paint is not the issue. I understand that even folks who try to adhere as close as they can to the prototype railroads also have "fun" in the hobby.
Rusty