Liz was a saddle tank engine who's Percy's sister and worked on the North Western Railway.
Technical Details
Basis
Liz is an 0-4-0 saddle tank believed to have been built by the Avonside Engine Company of Bristol, but prior to being purchased second or third hand by the Fat Controller he acquired components from Hunslet of Leeds and other builders.
Livery
Liz is painted in NWR light blue (formerly green) with red and yellow lining. His number 16 (formely 3429) is painted on the sides of his cab in yellow with red lining (formerly in black and yellow lining) and the lining around his cab windows is yellow.
Gallery
Thomas and Friends Fanfic Wiki has a collection of images and media related to Liz.