The color wheel is one of the easier ways to teach colors. Because the colors are placed according to the electromagnetic spectrum of light, your students will visually understand tone, hue and contrast from the wheel. You can print simple color wheels that diagram only primary, secondary and tertiary colors, or you can choose to print more complicated color wheels for older students that detail hues and shades.
Teaching students how to color mix (blue + yellow = green) is an important aspect of teach colors. You can find numerous color mixing printouts on the Internet that detail how primary colors render secondary color and how primary and secondary colors can create new tertiary colors. After reviewing color mixing with your students, you can choose to print out blank color mixing diagrams and pass them out to each child. With some crayons or colored pencils and the blank diagrams, your students can learn how to color mix themselves.
Understanding contrasting colors can be a little confusing for smaller children -- especially because contrasting colors are also referred to as complementary colors, which can be confusing in itself. Using a color wheel, explain to your students that the colors positioned opposite from one another on the wheel are contrasting (complementary) colors. These colors may be opposite ("contrasting"), but they also enhance the tones of each other ("complementary"). To explain this further, you use pictures of analogous colors, and then the same picture using contrasting colors to show how they create a bolder, more vibrant picture.
Have your students learn about colors by experimenting with different colors themselves. Print out several blank coloring sheets from the Internet, and hand them out to your students. You can choose to give them only primary colored pencils or crayons (or even paint for older kids). Tell them to color their coloring sheets in secondary and tertiary colors by color mixing themselves. You can also have them color their coloring sheets using only contrasting colors to enhance the look of the picture.