Wow. Not only is the stuff I wrote about still to be had, ZorkiKat also has its name. It's transparent (translucent, really, the same effect as gels most of the time) colours you want, which oils tend not to be. Mixing, come to think of it, may not be so difficult if you do it carefully on an easel. Poptart's worry is genuine, but there are ways to keep your colouring safe. Framing under glass (window mount) is the obvious one. There are also colourless sprays available which form a thin layer over a surface. You'll probably be best off with a non-glossy one, but that's a matter of taste. As a matter of interest, hand colouring B & W photos is something of an industry in my country. I haven't bothered to explore the thing, since the colours used are generally blindingly garish.