I also saw the ugly background now in some of my mails and in some email clients, results were also different by browser; so gmail in chrome was ok but not in IE. Got rid of it by removing <tbody> tags and generally porting the html back to the nineties, make your html as old as possible and it should work. There is also interesting information about what is supported of html in emails in http://www.campaignmonitor.com/css/
Hans