I ego-surfed for mentions of the 2 Tone Game, and found one: a post on an ARG (Alternate Reality Gaming) forum. (Thanks for that!) The poster there called the 2 Tone Game a "puzzle trail". Apparently, that's a genuine phrase that people use and stuff. It must be genuine, because I searched for it and I found stuff. E.g., I found the Blue Door Puzzle Trail. This is a series of online puzzles with some darned pretty art. I know, I know, I'm supposed to care about elegant puzzle design more than I care about graphical design. I promise I'll work on my attitude. Tomorrow. Meanwhile, I think these puzzles are purty. Check it out.