Order Confirmation and "Email a Friend" emails are hard-coded to have a white background. If you use white text on your store because you have a dark-colored theme, and the white text doesn't appear on your emails:
Go to Design > File Editor in your store's Admin Area.
Go through all of your email templates in /v/vspfiles/email_templates and find this line of code:
<link REL="stylesheet" TYPE="text/css" HREF="../../css/main.css">After the above line, add the following code:
<style type="text/css">body,table,td { color: #000000; !important }</style>