Teach your preschoolers about primary colors by giving them a bowl full of colored objects to separate and play with. Effective objects include poker chips, chocolate candies, large buttons or wooden beads in red, blue and yellow. Have the students separate them into bowls of like colors, and use them to make patterns or play a matching game. If you use wooden beads, they can string the beads in a pattern on shoe laces.
Build your students' vocabularies and their understanding of primary colors at the same time with color words. Introduce the colors red, blue and yellow to your students and have them talk about and list objects that are those colors. For instance, for yellow they might list the sun, sunflowers, bananas and lemons. Bring in items of each color for illustration.
Set cups of red, blue and yellow colored water at your students' tables along with plastic spoons and white paper towels or coffee filters. Teach your students how the primary colors blend together to make the secondary colors of purple, green and orange. Students can use the plastic spoons to put a few drops of red and blue next to each other on a paper towel or coffee filter and watch as they combine to make purple. They'll learn how blue and yellow make green, and red and yellow make orange, as well.
Finger paints are another way to teach preschool students how primary colors combine to make all the colors in the rainbow. Have them dip the fingers of their right hand in yellow and their left-hand fingers in blue paint. Instruct them to paint at the top center of a paper with yellow and the bottom left corner with blue. Get them to rub their fingers together to make green and paint a line between the blue and the yellow as one side of a triangle. After wiping their blue fingers, they can dip them in red to make the other corner of the triangle, and mingle red and yellow to make orange, and red and blue to make purple.