What did you do to your trains today?

Not just in Four Little Engines, but also in all their subsequent appearances. Even Rusty, whose name has nothing to do with rust, is originally black and not orange. However, Duke the Lost Engine (book #25) shows Stuart (Peter Sam) and Falcon (Sir Handel) working on the Mid Sodor Railway, and they were green and blue like in the TV series before moving to the Skarloey Rwy.
 

Thats a nice looking book Mr No, is it an old one?

Yes, it's one of the original Railway Series books the show was based on. This one's from 1955, but Mr. No has the 2018 reprint.