Apparently, the color green is taboo on magazine covers.  I had never heard this, but the opinion is, to quote Julia Turner, pervasive:

Cindi Leive, now the editor in chief of Glamour, remembers getting into "an almost physical fight" at Self over a cover that pictured Stephanie Seymour in a dark green sweater. "I liked the cover," Leive recalled. "But my art director … not only was she screaming, she was screaming in a thick and impassioned Finnish accent and telling me that dark green was the color of death …

[via DF]