Color Addition and Subtraction


Ask students to name the three primary colors of light versus the primary colors of pigment and you will likely find disagreement—these concepts are often misunderstood. Use this demonstration to help your students clearly see the difference between color addition and subtraction.


  • Additive vs. subtractive primary colors
  • Absorption and transmission
  • Complementary colors
  • Visible light spectrum

Experiment Overview

The purpose of this activity is to illustrate the difference between the primary colors of light and the primary colors of pigment. In the first demonstration, colored filters of blue, red and green will be used to show how combining the three primary colors of light produces white light. In the second demonstration, overlapping colored filters of cyan, magenta and yellow will filter out the wavelengths of visible light to produce black.


(for each demonstration)
Colored pencils (optional)
Lenses, double convex, 50-mm diameter, 3*
Overhead projector on moveable cart
Plastic sheet, white, with 3 cutout holes*
Projector screen or blank white wall
Tape, transparent
Theater gel filters, 2½" x 3", magenta, yellow and cyan*
Transparent acetate sheets, 3" x 3", red, green and blue*
*Materials included in kit.

Safety Precautions

This activity is considered to be nonhazardous. Follow all laboratory safety guidelines.

Prelab Preparation

  1. Using one of the holes in the white plastic sheet as a guide, draw a 2-inch circle onto the magenta theater gel filter and cut out the circle. Repeat with the yellow and cyan theater gel filters.
  2. Obtain the red transparent acetate sheet and trim it with scissors so it will cover one of the holes on the white plastic sheet. The piece should be large enough to completely cover one hole, but should not overlap any part of the other holes.
  3. Place the red transparent acetate sheet over one hole and secure the edges to the plastic sheet using transparent tape (see Figure 1).
  4. Cover the two remaining holes by repeating steps 2 and 3 using the green and blue transparent acetate sheets, respectively (see Figure 2).


Part I. Color Mixing by Addition

  1. Turn on the overhead projector and allow students to observe the white light emitted.
  2. Place the white plastic sheet on the overhead projector with the taped side down (see Figure 3). Red, green and blue light will be projected as separate circles onto the white projection screen or wall.
  3. Focus the circular images on the overhead screen. The three colors should still be projected as separate circles.
  4. Place a double convex lens over each transparent color circle on the overhead projector.
  5. Slowly roll the cart with the overhead projector toward the overhead screen. The colors will start to blur and overlap each other. Stop moving the projector once all three colors of light have merged together in the center to form white light.
  6. Students will observe that combining green and red light produces yellow light, combining blue and red light produces magenta, and combining blue and green light produces cyan (see Figure 4).
  7. Have students record their observations on the Addition or Subtraction Worksheet by labeling the diagram for Part I. Optional: Students may use colored pencils to fill in the diagram, matching the colors projected on the screen.
Part II. Color Mixing by Subtraction
  1. Remove the three lenses and the white plastic sheet with the colored acetate pieces from the projector stage.
  2. Obtain the magenta, yellow, and cyan theater gel filter circles.
  3. Place the yellow gel filter on the projector stage. Explain that the filter looks yellow on the screen because it absorbs blue light and transmits light in the ranges of the green- and red-light wavelengths (see step 6 and Figure 7 in Tips).
  4. Place the cyan theater gel on the projector stage next to the yellow filter. Explain that the filter looks cyan on the screen because it absorbs red light and transmits light in the ranges of blue- and green-light wavelengths (see step 6 and Figure 7 in Tips).
  5. 12. Ask students to predict what color they will observe when the cyan filter is placed so it overlaps the yellow filter and to record the prediction on the worksheet.
  6. Once the students have made their predictions, overlap the cyan and yellow filters (see Figure 5).
  7. Separate the cyan and yellow filters as in step 11.
  8. Place the magenta filter on the projector stage next to but not overlapping the other two filters. Explain that the filter looks magenta on the screen because it absorbs green light and transmits light in the ranges of red- and blue-light wavelengths (see step 6 and Figure 7 in Tips).
  9. Ask students to predict what color they will observe when the magenta filter is placed over the cyan filter and to record the prediction on the worksheet.
  10. Place the magenta filter so it overlaps the cyan filter and allow students to observe the color produced.
  11. Repeat steps 16–17 with the magenta and yellow filters. Note: For better results place the magenta filter on top of the yellow.
  12. Now ask students to predict what color they will observe when all three filters are overlapping and record this prediction on the worksheet.
  13. Arrange all three filters on the projector stage so they overlap, with the yellow filter on the bottom (see Figure 6). Producing pure black (absorbing all wavelengths of light) is very difficult with colored filters. As long as the three overlapping filters are surrounded by white light from the projector stage, the resulting color will be perceived as fairly black. In fact, some light is still transmitted (see Tips).

Student Worksheet PDF


Teacher Tips

  • The materials in this kit are completely reusable. Acetate sheets and theater gel filters may be stored in a plastic resealable bag or an envelope to prevent scratching or dust accumulation.

  • The lenses used in Part I refract the light being transmitted through the transparent acetate sheets. As the wavelengths of red, green and blue light bend toward each other, they overlap on the screen, producing the pattern seen in Figure 1 in the Prelab Preparation section.
  • In order to produce black, the primary subtractive colors must be saturated, each absorbing 100% of its respective primary color of light. In reality, this is hard to achieve. A chart of the transmission of each colored gel filter is seen in Figure 7. Note that visible light around the wavelengths of 480 (blue) and 590 (yellow) nm is not completely absorbed. Thus not all the light is absorbed when the three colored filters overlap and, instead of black, a dark muddy green may be perceived. For the same reason, overlapping complementary subtractive colors (see Discussion section) may not produce black. The cyan and red filters included produce nearly black when placed on an overhead projector and viewed on a white screen, but the complementary colors of magenta and green or yellow and blue are not saturated enough.


  • Show students a box from a tri-color ink cartridge. The colors shown are cyan (C), magenta (M) and yellow (Y). From these three primary colors of pigment all other colors may be produced. A black (K) ink cartridge is also used in color printers to save money from overuse of the colored inks. In addition, using completely saturated colors of cyan, magenta, and yellow to produce black would leave the paper rather wet, causing problems in the CMYK printing process.
  • Have students look at a color image on a computer monitor with a strong magnifying glass. They will see pixels of only three colors—red, blue and green.
  • It would be fun to combine this activity with radial paper chromatography of black markers. Chromatography will separate the pigments making up black ink. See Radial Chromatography—Chemistry with an Artistic Flair, Flinn Catalog No. AP8687 and Chromatography Challenge, Flinn Catalog No. AP7174.
  • The Flinn Color and Light Spectrum Demonstrations Kit, Catalog No. AP6172, may be used to further explore the visible spectrum.

Correlation to Next Generation Science Standards (NGSS)

Science & Engineering Practices

Asking questions and defining problems
Developing and using models
Analyzing and interpreting data

Disciplinary Core Ideas

MS-PS4.A: Wave Properties
HS-PS4.A: Wave Properties

Crosscutting Concepts

Cause and effect
Systems and system models

Performance Expectations

MS-PS2-1: Apply Newton’s Third Law to design a solution to a problem involving the motion of two colliding objects.
MS-PS2-2: Plan an investigation to provide evidence that the change in an object’s motion depends on the sum of the forces on the object and the mass of the object
HS-PS2-1: Analyze data to support the claim that Newton’s second law of motion describes the mathematical relationship among the net force on a macroscopic object, its mass, and its acceleration.
HS-PS2-2: Use mathematical representations to support the claim that the total momentum of a system of objects is conserved when there is no net force on the system.

Sample Data

Part II. Predictions

Yellow filter + cyan filter = green
Yellow filter + magenta filter = red
Cyan filter + magenta filter = blue
Yellow filter + magenta filter + cyan filter = black


Label each section of the diagrams with the colors observed. Optional: Use colored pencils to fill in the diagrams with the appropriate colors.

Part I. Color Mixing by Addition

Part II. Color Mixing by Subtraction

Answers to Questions

  1. What are the primary colors of light? The primary colors of pigment? Underline the primary colors in each diagram above.

    The primary colors of light are blue, red and green. The primary colors of pigment are cyan, magenta and yellow.

  2. Define complementary colors of light. Compare and contrast the complementary colors of light and the complementary colors of pigment.

    Complementary colors of light are two colors that combine to produce white. Complementary colors of pigment are two colors that blend to make black. The pairs of complementary colors of light and pigment are the same: red and cyan, magenta and green, and yellow and blue.

  3. What color would you expect to see if white light passed through a cyan colored filter placed on top of a red colored filter? Explain.

    Cyan subtracts red wavelengths of light and red subtracts green and blue wavelengths of light. Since all three primary colors of light are absorbed, no light is transmitted and black would be seen.

  4. Explain why the primary colors of pigment are also called primary subtractive colors.

    Each primary color of pigment absorbs or subtracts a primary color of light. Yellow subtracts blue, magenta subtracts green, and cyan subtracts red.

  5. Explain why the following statement is false. “The primary colors are red, yellow, and blue.”

    Blue pigment may be produced by combining cyan and magenta pigments. Red pigment may be produced by combining magenta and yellow pigments. Primary colors cannot be produced by combining other colors; therefore, red and blue cannot be primary colors of pigment. Red, yellow, and blue cannot be the primary colors of light since yellow light may be produced by combining red and green light.


The primary colors are a common misconception associated with color. Primary colors are colors that can produce a wide range of colors when mixed, but cannot be formed themselves by mixing other colors together. In other words, no primary color can be produced by a combination of two other primary colors. The primary colors of light are red, green and blue. These are often confused with the primary colors of pigments, which are magenta, yellow and cyan. The reason for the discrepancy is because mixing pigments follows a different pathway than mixing light. Blending colors of light form a color resulting from a process known as color mixing by addition. The color observed from the process of mixing pigments is the result of color mixing by subtraction.

Color mixing by addition takes place when the blending light is unmodified as it illuminates an object and reflects back to our eyes. This is observed when two colors of light superimpose on a white surface. The white surface reflects the wavelengths of light back to our eyes unaltered. The different wavelengths of light add together and our brain recognizes this “combination” wavelength as another color. For example, equal amounts of red-light wavelengths and green-light wavelengths add together and appear yellow. When equal amounts of red, green, and blue wavelengths of light are mixed, no color is seen as white light is observed. An interesting property of yellow light and blue light is that when equal amounts of these wavelengths of light are added together, again white light is displayed. Yellow wavelengths and blue wavelengths of light are known as complementary colors, found directly across from each other on the Additive Color Wheel (see Figure 8). Complementary colors of light are two colors that, when blended together, appear as white light. This occurs because the perception of the color “yellow” by our brain is the result of either ordinary yellow wavelengths of light reflecting to our eyes, or the result of the blending of red and green wavelengths of light. Our brain cannot tell the difference. Therefore, when equal amounts of yellow and blue light blend together, our brain interprets this combination of wavelengths the same as it would if equal amounts of red-, green-, and blue-light wavelengths were mixed—resulting in white light (see Equation 1).

Yellow + Blue = (Red + Green) + Blue = White
Equation 1.

Magenta and green, and cyan and red are also complementary colors of light (Figure 8).

{12087_Discussion_Figure_8_Additive color wheel}
Color mixing by subtraction occurs when the light illuminating an object is modified by the object before it reflects back to our eyes. Some wavelengths of the illuminating light are subtracted or absorbed. Paint pigments absorb and reflect a combination of light wavelengths. In a similar way, transparent colored filters absorb and transmit a combination of light wavelengths. As white light passes through the cyan filter, the color cyan is seen on the screen because the primary color of red light is absorbed, or subtracted from the incident white light. All the other wavelengths of light pass through the filter or are transmitted. The magenta filter absorbs the green primary color of light and the yellow filter absorbs the blue primary color of light. This is why the primary colors of pigment (primary subtractive colors) are cyan, yellow and magenta—they subtract one of the primary colors of light from white light. When two of these primary subtractive colors overlap, only wavelengths of light transmitted through both is seen. For example, when cyan and magenta overlap, both red- and green-light wavelengths are absorbed, resulting in only blue-light wavelengths being transmitted. When all three primary subtractive colors overlap, all wavelengths of light are absorbed and a complete lack of color—black—is seen. Complementary colors of pigments are two overlapping colors that produce black and are on opposite sides of the Subtractive Color Wheel (see Figure 9). Therefore, cyan and red are complementary subtractive colors since cyan pigments absorb red light and red pigments (a combination of magenta and yellow) absorb green and blue light.
{12087_Discussion_Figure_9_Subtractive color wheel}

Misconceptions about primary colors arise for several reasons. Many confuse the primary colors of light and pigment, not realizing the difference between additive color mixing and subtractive color mixing. A different color wheel, used by artists, is often taught in schools at the elementary level. In this case, yellow, red and blue are described as the primary colors of pigment, with purple, green and orange being the respective complementary colors. However, red can be produced by mixing magenta and yellow pigments and blue can be produced by mixing cyan and magenta pigments; therefore, neither red nor blue are true primary colors. Mixing complementary colors from this color model produces brown, not black.


Woolf, L. D. Confusing Color Concepts Clarified. The Physics Teacher. 1999, 37, 201–206.

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