Make a gooey concoction as the base for mixing colors. Place a cup of cornstarch into a bowl, and slowly add water until you've created a thick concoction that has the consistency of syrup. Have two preschoolers each choose a primary color of food coloring, which include red, yellow and blue. Ask the two children to predict what color they'll make and then squirt a drop or two of their color into the bowl. Encourage the preschoolers to squeeze the mixture with their hands to incorporate the colors, revealing the new color. Do the experiment several times so preschoolers learn that mixing different combinations of colors creates various hues.
Sidewalk paint is easy to make and provides an artistic medium for experimenting with color mixing. Combine equal parts cold water and cornstarch as your base. Divide the mixture among several bowls or sections of a muffin tin. Allow the preschoolers to squirt two primary colors into each section to create new colors of paint. Alternatively, make primary colored sidewalk chalk, take it outside and encourage preschoolers to use paintbrushes to paint creations on the sidewalk, mixing the colors as they go. Talk about what happens when they mix certain colors together and invite them to tell you what two colors made the new colors.
The science part of this activity is mixing cornstarch, water and food coloring in squeeze bottles, such as empty ketchup or salad dressing bottles. You don't have to measure the ingredients exactly, which is part of the scientific process, too. Put some cornstarch into each squeeze bottle and add just enough water to make a thick solution that's still thin enough to squeeze out of the hole in the bottle. Let the preschoolers add red, blue or yellow food coloring to the bottles, close the lid tightly and shake the bottles gently to mix the color in. Then ask the preschoolers to choose two primary colors to add to additional bottles and repeat the shaking process to make orange, green and purple. In the end, you should have six bottles with red, orange, yellow, green, blue and purple paint. Take the bottles outside and let the children paint rainbows on large pieces of cardboard or card stock. This is a good time to remind preschoolers of the order of colors in a rainbow.
Cornstarch is an effective tool for color mixing experiments, but it's not the only one. Fill ice cube trays with water and let preschoolers add food coloring to each. Encourage them to make some with one color and to mix colors in others. When the ice cubes are beginning to harden, poke a wooden craft stick into each and let them finish freezing. Pop the cubes out of the tray and let preschoolers use them like paint, asking them about the colors they notice as they create their pictures. Squirt a tiny drop of one color of washable paint into one of a preschooler's hands and another drop of a different color into her other hand. Have her wash her hands, revealing a new color of soap suds. Put shaving cream into a sensory table and let preschoolers add two colors of food coloring or washable paint. Then the children can use their hands to mix the shaving cream, revealing a new color.