Colors of M & Ms and Skittles

Dr. Frank Walmsley

Trinity University

San Antonio, TX 78212

The Rainbow

The Rainbow As Seen by a Scientist

When the eye sees all the colors of the visible spectrum, it sees white light.

The Colors of M&Ms and SkittlesThe Dyes Used in Manufacture

• Red Red

• Blue Blue

• Yellow Yellow

• Green

• Brown

Why are Red M&Ms Red?

• A red object or a red solution is red because the eye sees the red light portion of the visible spectrum.

• The other portions of the spectrum are absorbed by the object or solution and do not reach the eye.

A solution in a cuvetteThe colored solution is to be measured.

The colorless solution is a reference.

Light of varying wavelength pass through each solution and the difference is recorded.

A Red SolutionSome red color is dissolved from the coating

of red M&Ms.

The SpectrometerThe visible spectrum from 400 nm to 700 nm is recorded by

a spectrometer.

The spectrum shown on the screen is not the red solution.

The SpectrumThe spectrum of the red solution measured from 400 nm to

700 nm. Notice no light is absorbed from about 600 nm to 700 nm. This is red light.

This light not absorbed

This light absorbed

Why are Blue M&Ms Blue?

• A blue object or a blue solution is blue because the eye sees the blue light portion of the visible spectrum.

• The other portions of the spectrum are absorbed by the object or solution and do not reach the eye.

Preparation of a Blue SolutionTwo M&Ms placed into water after about 5 seconds. Some

of the dye is already dissolving.

A Blue SolutionA solution prepared by dissolving some

coating from blue M&Ms as shown in previous slide.

Spectrum of Blue Solution

The spectrum of the blue solution from 400 nm to 700 nm. Notice that little light is absorbed between about 420 and 470 nm; this is blue light.

This light not absorbed

This light is absorbed

How Do You Get Green M&Mswithout Green Dye?

Can you combine colors?

Which ones?

Right!

Yellow and Blue make Green

Preparing a Green SolutionDissolving the coating from a yellow and a

blue M&M. Notice the green solution forming.

A More Fundamental Question

WHY do yellow and blue make green?

Yellow Dye

Blue Dye

This part absorbed This part absorbed

This part not absorbed

Yellow and blue make green

Because the yellow and blue dyes

absorb all the colors of light except green.

Brown is not a primary color.

It is a specific combination of other colors in specific quantities.

Preparing a Brown Solution

The coating from brown M&Ms is dissolved in water.

A Brown Solution

The solution from brown M&Ms appears sort of orange because of its low concentration.

A Black Solution

How would you make a black solution?

What would the visible spectrum look like?

Preparation of a Yellow Solution

A Yellow Solution

Spectrum of Yellow Solution

A Purple Solution

Prepared by mixing red and blue solutions.

Spectrum of a Purple SolutionNotice that there is little absorbance near 400 to 430 nm compared to

large absorbances of the red and blue dyes. Notice the wavelength scale is not the same as the other spectra.

Structure of Red 40

Structure of Yellow 5

Structure of Yellow 6

Structure of Blue 1

Structure of Blue 2