Did you know you can use Play Doh to teach students about mixing colors? A very tactile experience!
Start with two colors of Play Doh (I'd recommend beginning with primary colors, you can expand from there). Use a small amount of each color.
You'll see the colors swirl together at first, and then combine to form a new color:
Here it is next to a sample of the original colors, so you can see what happened.
You could have a lot of fun creating a Play Doh color wheel, or varying the amount of each color you used to create a whole range of shades.