I want to hide my trivia answers on the cards. The players would have to use the decoded lens (e.g. red plexiglass) provided over the card to get the answer.
What is this method called, where can I get information about it, and how is it done in Adobe Illustrator?
Simply put: For a red lens and a white background you want blue/green text and red noise on top of the text. Through the lens the red and white will look the same, while the blue/green will stand out.