This was fun activity that I got from Roper Mountain Science Institute. They suggested red theater gel to reveal the message, which can get pricy. Another idea I heard was to ask movie theaters to donate left over 3D glasses, which also have a red filter. A guest speaker we had last year said red jello would work. Tried it this week and it worked like a charm. The students thought it was very cool. I found my "attention challenged" students had trouble focusing on making their own secret messages so I was very glad that I had made extra copies of the sheets from the GEMS Color Analyzer book that they could color and then check under the jello.

Comments
useful for you. You convert it to pdf
and you post such that it will be helpful for others.