The Southern Methodist University (SMU) has digitized a collection of Baldwin Locomotive Works engine specifications from 1869 to 1938. Below is a scan of the page for Niagara Junction Railway locomotive #1, ordered in September 1899.
It is designated as a class 6-30C. The leading “6” indicates the total number of wheels, the “30” is the size of the cylinder, and “D” indicates there are six driving wheels – a 0-6-0 locomotive. Trains magazine has a good article on how to decipher Baldwin classes.
The locomotive was painted olive green and aluminum, had the name “Niagara Junction Railway Company Co.” painted on the tender and the number 1 painted on the dome on top of the locomotive, on the back of the tender, and on a number plate on the front of the locomotive.
Source: Baldwin Locomotive Works engine specification, volume 22, page 226 (page 169 of the PDF file). From the collection of Southern Methodist University libraries.