You will need:
1 piece of heavy, smooth paper (posterboard, piece of a manila folder or card stock computer paper)
black or other dark color tempera paint (I get mine from the dollar store) - Optional
Color the paper brightly by pressing down hard with the crayon. Leave no uncolored space. (with the purple butterfly, I stopped the preparation here.)
For the black ones, I made spots of different colors. Mix the tempera with a few drops of dish soap (allows it to stick to the waxy crayon surface) and paint over the entire thing. Wait for it to dry.
Use paper clips, butter knives or whatever to draw your image.