clipped from pwbeat.publishersweekly.com

In an email Nat Gertler speculated the production error:

“Just having looked at scans over the Internet, it looks to me like the lettering is printed using just black ink, while the bars were put on a different layer using “rich black”, which is a mixture of all four color inks. “Rich black” makes a darker, more vibrant black. On the computer screen, it would all just look black, but the difference will be visible on the printed page.”