In honor of St. Patrick's Day we created a Walking Rainbow.  We started with 6 pint jars.  Three of the jars were filled with water.  We added the primary colors (red, blue, and yellow) to those jars.  We placed the jars in a circle with an empty jar between each.  I rolled a a paper towel tube connecting the jars.  Throughout the day we watched the colored water travel to the empty jar through the paper towel tubes.  By the end of the day, enough water traveled into the empty jar to create the secondary colors of green, purple,and orange.  It's a crazy cool experiment.