Created this light in my dorm room during my sophomore year in college.

Material: LED, copper tape, magnet, scotch tape, battery

I started with only white and blue LEDs because they can be lit in the same circuit. 

Then I added another strip of copper tape on the top to include yellow lights. Since yellow LEDs require less voltage than white and blue, they need a separate circuit. Two circuits share the same positive path. The color can be switched by changing which copper tape attaches to the battery.