The visible light spectrum is the arrangement of colors from red to violet.  The colors in the visible light spectrum are red, orange, yellow, green, blue, and violet.

Some people still think that indigo is a color in the visible light spectrum.  Indigo was removed from the visible light spectrum because its wavelength falls very high in the violet range, near the lowest end of the blue range.  Few people, if any, can differentiate the wavelengths so precisely that they can perceive a separate color between the blue and violet ranges.  Indigo is still a color, but not one on the visible light spectrum.

Watch the video to see the visible light spectrum using a diffraction grating.

When two colors are added and white light is formed, they are said to be complementary.  When you look at the picture, the colors that are across from each other are complementary.

Green + Magenta (which is red and blue) = white light

Blue + Yellow (which is red and green) = white light

Red + Cyan (which is blue and green) = white light

Watch the video to see a demonstration on additive colors, which are colors of light.  We call them additive colors because we add colors to each other to get a new color.  It is very important to know this color wheel to be able to answer questions on color addition.

Colors of light and paint are two different things.  The primary colors of light are red, green, and blue, because when you add them together at the correct intensities, they make white light.  If you add red, blue, and green paints together, they absolutely do not make white paint.  That is because paints have dyes and pigments.

A dye is a molecule that absorbs certain wavelengths of light and transmits or reflects others.  A pigment is colored material that absorbs certain colors and transmits or reflects other.  Pigments are larger than dyes.  Some materials use pigments and others use dyes, it depends on the chemical make-up of the material.  We will not be going into material chemistry in this class.  All you need to know is that dyes and pigments control the color of objects.  

A tomato is red because it absorbs blue and green and reflects red.  The color we see is the color(s) that are reflected.  The colors we can't see are absorbed.  Bananas are yellow because it reflects red and green and absorbs blue.

When we look at colors with dyes and pigments, colors are being subtracted out, or absorbed.  That is why it is called color subtraction.  

A primary pigment is a pigment that absorbs only one color from white light.  Yellow, cyan, and magenta are primary pigments.  This is because each of these pigments reflect two colors and absorb one.  Magenta absorbs green and reflects red and blue.

A secondary pigment is a pigment that absorbs two primary colors and reflects one.  Red, blue, and green are secondary pigments.  Red absorbs blue and green and only reflects red.

To recap:  

Primary Subtractive Colors (Primary Colors of Paint):  Yellow, Magenta, and Cyan

Secondary Subtractive Colors (Secondary Colors of Paint):  Red, Blue, and Green

Pigments subtract colors out by absorbing them.  Please watch the video to see color subtraction in action.  Knowing your color wheel will help you with color subtraction questions.

Click on the picture to take you to the color wheel that you need to know before class starts.  Knowing this color wheel will make it MUCH easier to answer questions on color addition and subtraction.

We will be completing this in class.  See if you can get the answers correct now!

Be sure to head over to google classroom and fill out the exit pass.