Just been looking at archive footage and stills of COTN, and it seems to me that the handrail along the boiler is green, not silver / steel / chrome as on the upgraded Hornby offerings. The reason it looks lighter than the body colour is because being a curved surface, it has a highlight from the sun / sky. In a close-up shot from the front where the rail is vertical, it seems to be the same colour as the smoke deflector behind. It wasn't common for LNER locos to have natural metal handrails, especially the apple green ones.
Quite happy to be proved wrong here, but in a way, the green hand rail on the railroad version looks the more realistic to my eye.