I saw something like this at the Children’s Museum we go to and decided to try it out with my son. I placed water with different colors of food coloring in an ice cube tray. I left some of the spaces open so he could mix new colors in the empty spots. I had a squeezable tube from a different art project that we used. You could use anything like an old Tylenol dropper, the squeeze kind, or the kind where you pull it up to grab the water and push it down to release the water (an old one!). I helped my toddler squeeze the tube to let the water in (my hand over his) and then he squeezed it all by himself into whichever spot he wanted to. He had a lot of fun doing this and cried when I took it away because we were all done. It was fun for him to see the colors mix together!