A while back, Matthieu Lachance was kind enough to prepare the artwork for the CV steam locomotives in this era (there was an even earlier CV steam lettering style, shown below on 4-4-0 no. 100), but the style in the artwork and shown on no. 101 above dates to 1900, and lasted up through the mid 1930s with some variations. 
I don't know what color the lettering was.
My best guess is it was either some form of "white" - even a very light gray. I don't think it would have been aluminum paste lettering, like that found on Santa Fe locomotives up through the end of steam.
Or the lettering was some version of yellow - "Deluxe Gold" - best described as "mustardy" yellow and applied to Pullman and other passenger cars starting in the early 20th century.
I don't think it would have been gold leaf - which would appear like glittery gold lettering - since gold leaf was more expensive and likely went out of style about the same time locomotives lost their Russia Iron boilers jackets.
Perhaps in-depth examination of the railroad's accounting records would reveal if, and when, they bought a particular stock of paint for the locomotive shops. Perhaps, but I simply don't have the resources or information to conduct such detailed research.
Of course, it's also possible they did something like apply gold lettering to passenger engines, and white to freight hogs.
I have reached out to some experts in the railroad's early history to see if they can offer any insight. Otherwise, I'll figure it's a best guess and press on. I know which way I'm leaning. I'm leaning towards some form of yellow lettering, , but that's wishful thinking based on the fact I think the locomotives would look sharp - but I have absolutely no evidence to support that choice.
Come to think of it, I have no evidence to dispute it either!
Maybe I should have the decals printed up in both colors to hedge my bets?
