Be sure to have several small manipulatives in your classroom that you can use for teaching colors. Beads or blocks work well for this activity. Jumble all of the small pieces together and ask students to sort them by color. You can also test knowledge by asking each student to take all the pieces of a particular color.
Students will enjoy seeing how two different colors mix together to form a new color. You can do this with colored glass or you can use paint. If students don't yet know about how colors blend to form new colors, you can put a dab of paint in two primary colors onto their paper and ask them to see what happens when you mix the two.
You can find many books that teach the concept of colors. Try to keep your students' interests or other themed units in mind when you look for these books. For example, a book about growing flowers in every color will also work well with a spring theme.
Create simple flashcards by cutting rectangular pieces of construction paper and laminating them. Hide one set of the cards somewhere in the room, then hold up one and challenge students to find its match. You can also hold up a color and have students try to touch something else in the room that matches that color.
Printable worksheets can also reinforce the concept of colors. Try finding the coloring sheets where a picture emerges as students follow the coloring key by coloring all number ones the same color and so on.
If you have a class station for file folder games, you can create a few file folder games that help teach colors. For example, you could create games for color matching, color mixing or color identification.