one of the easiest ways to get great skin tones on your black and white copies without too much fuss or thought is to simply use copic markers. (www.icopic.com) copic colors are permanent, juicy, consistent in color (because they are machine made), bleed proof and streak proof and can easily be painted over with water based paint, with or without using matte medium.
the markers i use are dual tips. i use the broad chisel tip sketch markers to do quick clean swipes of color down the face and limbs of the figures in the picture, not caring if i swipe outside of the lines because i will be painting over any mistakes when i fill in the background colors using acrylic paint.
i always copy my images on 20lb bond paper - i do not use matte medium for this process.
i have listed a few colors i have in my collection that i use frequently. in this particular black and white image, i used only 3 different skin tone colors. one color for each person since we were all different shades of white.
for mom, i used EOO "skin white", my brother who is tan, YROO "powder pink"and me, the little baby, ROO "pinkish white". you might think, why didn't lisa use "baby skin pink" for herself as a baby? well, i tested the colors and "baby skin pink" was not only to dark for me, but also too dark for my tanned brother.
the color i have here are:
ROO pinkish white, YROO powder pink, E00 skin white, BV31 pale lavender, E21 baby skin pink, E20 blush, RO2 flesh, and E34 orientale. if you are interested in copic markers, try a kit, or do what i did, go to the nearest (blick) art store or go online and select the lightest colors you can find for the skin tones you are painting.
oh yeah, you might wonder why i have a pale lavender in my skin tones. i use that for shading in the darkest crevices of the neck and hairline. the biggest caveat i can think of is this: be sure to use the lightest colors you can in the hue of skin tone you want to use. since these colors are juicy, it doesn't take much for the paper to absorb extra ink and give your image's face a synthetic look.
let me know if you have any questions.
later i will tutor you on using and mixing paints to achieve skin tones instead of using markers.