Silver is a narrow gauge engine, who was renamed Tramp.
Silver is a narrow gauge engine BoCo once mentioned in a story he told Skarloey. Apparently, Silver was the fastest engine in the hills, with silver paint to suit his name, and was always boasting to the other engines. At last, a wizard was tired of Silver's boasting and put a spell on him, turning Silver into a rusty slow engine. He became the laughing stock of the other engines and was renamed Tramp.