(Idea originally conceived in 2009)
I’m fascinated by color. When I was younger I dreamt of discovering a color that nobody has ever seen before. And since most computer languages give you easy ways to manipulate graphics, I played with color on a computer.
One day I saw an interesting effect on some certificate I received. When I photocopied it in black and white, a word appeared in the photocopy ("COPY") that wasn’t visible in the original. This "security measure" took advantage of the photocopier’s inability to faithfully replicate the document (the word COPY was actually visible in the original but it was difficult to see because it consisted of a myriad of tiny dots). I wondered whether it would be possible to hide messages in documents even if the copier were to produce faithful facsimiles, but converted color to black & white images.
In this first experiment, text is visible in a color image, but when you render the image in black & white, the text will disappear.
In the second experiment, text is only visible once you render the image in black & white. I've added a "distraction" text that you will see in the color rendering. (On your computer screen, you may still see both strings because of your browser's image color correction or color variability of your LCD screen. But if you print the image out in color, you will only see the "distraction" text.)