The first thing we did (24 hours before we painted) was put water in the ice cube trays and then we added food colouring. My son told me the names of all the colours and my daughter "taught" me how to make purple, orange and green by mixing colours. I used one of our chopsticks to stir the food colouring in each of the cubes. Then we put the coloured water in the freezer.
The next day, it was HOT out. We went outside and sat on the ground with our "paint shirts" on (plus sunscreen - and lots of it!). I have watercolour paper at work, so that was what we used. Regular paper will probably not work, but try it! The original post used white fabric, which would have made a really cool keepsake! The ice cubes melted REALLY fast but the kids made some beautiful artwork! Definately a hit and I can't wait to do it again with my preschoolers AND with my own kids again next summer!