Another tip re: handcoloring is doing multiple layers. If you can't get the intensity you want of the colors using regular oils, you can let the print dry for a while, then do a 2nd layer of color over the first. It will add to the intensity of the color. I did a whole series of handcolored prints back in the early 90s, and may get back into it again sometime. Probably not that many people doing it anymore, these days.