Casey:
I have included a color photo of Durango here for you to refer to. While the original C-25 photo you colorized was circa 1948 the below view is circa 1965. Now here is where we start down the slipperly slope. Was the color of paint used on the structures the same between the years referenced and did all the structures use the same color of paint etc. etc. How do you pick the color in the program you are using and what type of color matching is done?
Jerry Day posted a link to a site about the commercial use of digital files and here is another one dealing with many of the formatting and technical issues that are part and parcel of this discussion.
[www.updig.org]
I have been Googling trying to find some technical reference, industry standards or archival recommendations for color conversion of B/W photos to color without results.
Casey, I am glad you have opened this can of worms so to speak. What my hope would be is that you can blend your creative talents with historical reference materials to achieve an end result that will not only have artistic value but lasting historical value as well.
John West photo, Durango ,CO September 1965