Last Sunday, I settled on the grass next to the Washington Monument to watch the Fourth of July fireworks, armed with a pair of diffraction glasses. Diffraction glasses, sometimes called rainbow glasses, have a special plastic lens which splits white light into the whole visible spectrum. Each lens has thousands of microscopic slits that cause the lens to act like a prism when light hits them. The colors in the rainbow you see are even in the order you learned in kindergarten with ROY G BIV--red, orange, yellow, green, blue, indigo, violet. This is the exact same process that happens when you see rainbows after a storm. In the case of rainbows in the wild, white light from the sun gets diffracted through the raindrops in the air. The rainbow that you see through diffraction glasses is called a spectrum.
Because white light contains all the colors of the rainbow, you see all the colors when it gets diffracted. Everyday lights, even colored ones, shine in more than one single color, even if it seems like one color to you. If you look at a blue light through diffraction glasses you only see the colors that make up that particular blue--usually green, blue, and indigo. The other colors of the spectrum will be absent. The same thing will happen if you look at an orange light. You will only see red, orange, and yellow in the diffraction glasses.
Lasers are a special type of light that only emit in one color. If you look at the light from a laser using diffraction glasses, you will only see a single dot in the laser's spectrum, the same color as the laser.
Here's a few more pictures of diffracted fireworks.
