I have been trying to find any information on how to print secret messages. The concept is simple, print a message in red with a blue pattern over the top to disguise the message. The recipient would then use a blue-filmed set of glasses to filter the blue pattern and reveal the message. Over the years, I have subscribed to over a half dozen different design magazines and could have sworn I saw a how to article on this very subject. But, wouldn't you know it, when I actually want to attempt this technique, I can't find the article.

Thanks for any assistance you may provide.

Mark