Change to blank cover behaviour in 3.7

Prior to my upgrade to 3.7 (on Mac) a book with no cover would have a literally blank cover image, with no file associated with it. Since the upgrade, I get a blue image with a curlicue border. Remove cover produces the same image.

Is there any way to get the old behaviour back? I have searched the forum here, as well as the Calibre Preferences without success.

:help: