This is how I used to color my art: cutting out piece after piece of Letraset colored film, lightly attaching each piece, trimming away the excess, then burnishing. I'd usually add some shading beforehand using colored pencils. After many years, that painstaking process drove me batty enough that I switched over to watercolors. These days I scan my drawings into the computer and color there.
I'm not sure who took this photo, or why, but I found it while searching through a closet for something else.
This was a 1985 poster for New York City's Charter Revision Commission. To see the finished poster: CLICK (and then click on the poster to enlarge)