Harshness of red marks has students seeing purple: "A mix of red and blue, the color purple embodies red's sense of authority but also blue's association with serenity, making it a less negative and more constructive color for correcting student papers, color psychologists said. Purple calls attention to itself without being too aggressive. And because the color is linked to creativity and royalty, it is also more encouraging to students.
"'The concept of purple as a replacement for red is a pretty good idea,' said Leatrice Eiseman, director of the Pantone Color Institute in Carlstadt, N.J, and author of five books on color. 'You soften the blow of red. Red is a bit over-the-top in its aggression.'"
Me thinks the meaning is getting lost along the way. Red is for mistakes. Blue is for annotations. Purple blurs the distinction, making the mistakes seem less wrong somehow. This doesn't make corrections made in purple any less valid, but sometimes you really want a color that screams out WRONG!