You will need crayons, a pencil, and white paper for this craft.
Start by coloring one side of your paper either in patterns or blobs, however you wish, just as long as you press hard and cover the whole area in crayon. The picture below shows an example of this started.
Lay your pattern face-down on top of another blank sheet of paper. On the back, draw a design in pencil. ( You can see the colors from step one on the back side of this page below)
Lift up your paper and check out your design! You will see that your pencil drawing transferred to the other page in the colors you drew. So it will look rainbow-like.
Have fun experimenting.