Many years ago, when color films were not so prevalent, portrait studios made black and white photos, and colored them with Marshall's oils. I worked in that medium for a studio in 1952, and achieved some nice results. It usually helped if the prints were sepia toned before coloring. Used a lot of cotton swabs doing it, and also wound the cotton on larger, pointed sticks. I still have a portrait of me that my parents had made when I was a small child at age 18 months. The color still holds up after 74 years as it was back then.

So, give that kit a try. If you goof, the oils can be removed before drying using the medium in the kit.