I just finished an icing lesson today with 6th graders. I was working with the Family/ Consumer Science teacher. Her kids baked and mine decorated using "color theory", then presented their color concept to both classes while we enjoyed the cookies.
Frosting receipe (frosted 78 cookies-- barely) 3 cups shortening and enough powdered sugar to make it stiff and spreadable, food coloring or frosting color concentrate.
It was a MESS, but the kids seemed to love it (all but the presentation!!!)