The Rainbow Sun is Billy Twofeathers' locomotive and is one of several that run on the Indian Valley Railroad.
In the opening sequence for Shining Time Station, it was portrayed by the Union Pacific #844, a 4-8-4 locomotive built in 1944 which was the only steam locomotive in the US to operate continuously since entering service, having never been retired. The 844 is still active today as part of the Union Pacific's steam program. In Thomas and the Magic Railroad, it was portrayed by the Strasburg Rail Road's #475, a 4-8-0 locomotive built in 1906 and formerly on the roster of the Norfolk & Western Railway. It is one of only few N&W 4-8-0 Mastodon locomotives preserved, and the only one of its class operating. #475 is still operating today as one of Strasburg's main locomotives.
The Rainbow Sun is painted black with yellow lining and brown window frames. The number "475" is painted on the sides of its cab in gold.
- The whistle sound used for the Rainbow Sun is later used for Rocky in Edward Strikes Out, Victor on the Guess Who? Puzzles, Timothy on the Official Website, Ferdinand but at a lower pitch, one of the steam engines in the Down at the Station segments, Carlos in The Great Race, and Lexi from Journey Beyond Sodor. This sound is often used in TV and film, originating from the sound effects company Sound Ideas.
- The Rainbow Sun was seen in the Thomas and the Magic Railroad (activity book) but it was illustrated as an E2 class tank engine like Thomas and has the number 90 just like the Strasburg Rail Road's ex-Great Western No. 90.
- The coaches that the Rainbow Sun pulls were originally going to be three coaches, but only two coaches were used.