Colored blocks work well for helping kids differentiate between colors. Most classrooms have some sort of colored blocks to use for the activity. You can also use other multi-colored items such as craft pompoms or beads. Have the kids sort the blocks or other objects into separate piles based on color. A preschooler who can successfully sort out the items demonstrates that he understands the differences in color even if he can't put a label on it. Once you create the piles, ask the child to tell you the name for each color pile.
File folder games are homemade activities that store well in the classroom. A plain manila file folder creates the game board. A simple color file folder game is a matching game. Place pictures of different colored objects on the file folder. Create separate playing pieces shaped like crayons. You'll need one of the crayons in a matching color for each of the objects on the file folder. Write the color name on the crayons so they become more familiar to the students. The kids place the crayons on top of the corresponding pictures to match the colors.
A color scavenger hunt helps the kids find different colors in the environment. As you call out a color, the preschool kids look around the room to find something of the same color. You can also use color cards to help the kids locate items. Hold up or pass out a specific color card. The kids find an object in the same color and state the name of the color. See how many different objects the kids can find for each color you name.
There are many color books available at the average library. Instead of always reading one of them, make your own classroom color book. You can make one large book as a class or make individual books with the kids. Make a page template for each of the colors. Leave a square or circle so that the kids can use a crayon to fill in the shape with the corresponding color. You can also have the kids cut pictures out of magazines for each color and glue them to the corresponding pages.
This game tests the ability of the students to match the colors with the name. Paint or draw with a marker on paper plates, one for each color you're practicing. Place the different colored paper plates in a circle on the floor. One child stands in the middle of the paper plate circle. The teacher calls out a color. The child points to the paper plate with the corresponding color.