Hang posters and signs around the classroom that show the colors of the rainbow and their names. Make easy signs yourself by cutting shapes out of colored paper. Write the name of the color onto each shape. Laminate the shapes, then tape them low on the wall. As you play on the floor with children, occasionally point to a shape and ask them what color it is. Give them the answer if they do not know.
Read books about colors. Visit the local library to borrow board books or story books about colors, such as "Brown Bear, Brown Bear, What Do You See?" by Bill Martin, Jr. and Eric Carle. You can also create your own books. Take photos of colored objects. Group the photos together by color, then print each set of photos on a separate page. Laminate the pages, punch holes in the left side of each page and tie the book together with yarn.
Choose a color of the day and make it your theme that day. Send home a note to parents with a schedule of your color days so they can dress their children in that color. On each color day, eat foods in that color and create art projects using colored paint or markers.
Play "I Spy" with colors in the classroom. Gather children together and say "I spy with my little eye something green." Have children look around the room, then guess which green object you had in mind. This requires children to notice all the objects that are the same color.
Talk about primary and secondary colors. Once children have learned to identify each color, explain that some colors are formed by mixing other colors. Give each child some food coloring and an egg carton with a bit of water in each section. Let children experiment with mixing different shades together in each section. You can also teach about color mixing by letting children mix paint shades together. Ask them to observe which colors they can and cannot create by combining other colors.