Data Visualization on the cheap

Well, I may be the last person in the world to learn this, but newer versions of Excel now let you apply more than two conditional formatting rules. I was making a chart counting the hours of the week when our "Ask a Librarian" questions come in by email, and thought I'd highlight the busiest times with a conditional formatting rule or two. But it turns out, for this chart at least, that setting up four easy rules is all it takes to make it into a passable heat map: