A toilet paper roll
A CD (make sure it´s one that nobody needs!)
Stick the insulating tape on the CD and then remove it to leave the CD transparent. Repeat until a large area of the CD is transparent.
Place the toilet paper roll on the transparent area of the CD and draw a circle around the toilet paper roll. Cut out the circle carefully with the scissors.
Use the insulating tape the stick the edges of the transparent circle to the top of the toilet paper roll.
On the opposite end of the toilet paper roll stick some more insulating tape and leave a small hole to look through.
Decorate the outside of the roll if you wish.
Look, through the small hole, towards the light. What can you see? A rainbow!