Although I haven’t hand colored a print in years, I have done it quite a bit. I started out using the Marshalls Oil paints but found the results less than satisfying: it always seemed that the colors sat on top of the image and never really integrated with the photograph.
Years later, when I worked as Deborah Samuel’s darkroom technician, I learned from her how to color using watercolors. It was a painstaking process which required that you layer on very dilute color over and over, gradually building up saturation to get a believable result. The print has to be kept slightly damp as you work, and to make the colors integrate best, we would do a very light sepia toning of the print to prep it for coloring. The colors always seemed to integrate better into the image if applied to a warm tinted print. Perhaps the Marshalls colors would have worked better on a sepia tinted print.
I hope that helps.