Interesting color chart...
A couple of observations: Assuming these paint chips are what the D&RG had for a color pallet in C. 1915.
On my laptop ( not perfect color calibrated like my studio monitors )... My attempt to adjust the .JPG posted photo, came right near to what Joe W. posted. The original posting is rather not to far off for density or coloration, but typically a bit contrasty from the slide reproduction. With that said, there isn't much more in the color department we can learn from that scan.. It appears the worker is sanding down the base metal of the tender, and having left the numbers, and a bit of background paint around each number, which is why it appears that the numbers have a "Outline" around them. The Photo was taken in what would be call f/16 light ( SS of 1/asa, full sun, bright shiny day with hard crisp shadows ) the image isn't to far from looking correct, with the noted contrast bump, even the skin tone isn't too bad, and the well used alum. ladder looks neutral enough for a ok color basis.
Looking at the paint chips photo ( which on my laptop ) the 18% gray reference appears a touch darker then 18%, and so lighting the image so it appears 18%, gives me a good idea as to the chips tonal color. I can clearly see why the artist that painted the turn of the century painting of the D&RG engine would use what the layman would call light orange paint, if the D&RG used the " Chrome Yellow Lemon" paint. I think most of the public would refer this color as "Gold" when laid on a black background. From more then a few feet it would certainly appear as gold lettering to most ( my speculation ). But the color contrast between the numbers and the black paint would be a bit low, especially at night under lower light conditions.
If the RR used the " French Chrome Yellow", That lighter and more commonly called "Yellow" Paint, these numbers would clearly of "Popped" off of the black Background, and been much more visuable from a greater distance then the "Chrome Yellow Lemon", but not appear as "Rich Looking" ( again my assumption ).
Which one is it... I don't know ... but if the RR was trying to replicate Gold leaf on the numbers... Thou looking a bit golden in tone ( Chrome Yellow Lemon ) I don't think under most conditions it would fool anyone as being Gold Leaf. But a viable color subistute. The Superintendent referring to "Yellow" paint... leads me to think that he was referring to the " French Chrome Yellow" as generic yellow. The "Chrome Yellow" would generally be referred to as "Orange" And I don't see any of that tone in the photo. Again My speculation and assumptions.
If I had to vote... Using the included pallet... it would be for the French Chrome Yellow...
Your thoughts welcomed.
Dave