This may happen if background images are turned off in Internet Explorer settings or by a plug-in (several ad-blocking plug-ins are known to do it).
To check Internet Explorer settings:
1) Select Tools > Internet Options... from the Internet Explorer menu
2) On the General tab, click Accessibility
3) Make sure 'Ignore colors specified on web pages' is not selected
To see the list of installed plug-ins, select Tools > Manage Add-Ons... from the Internet Explorer menu. They can temporarily disable any suspicious add-ons and see if it fixes the problem.