I think you need to grab the entire ".featured-wrapper" blog as set by the theme and update each color code inside. Here is an example:
background: -webkit-gradient(linear, left top, left bottom, from(#5b3d5a), to(#473246));
background: -moz-linear-gradient(top, #5b3d5a, #473246);
filter: progid:DXImageTransform.Microsoft.gradient(startColorstr='#5b3d5a', endColorstr='#473246');
border-top: 1px solid #6aa3df;
The "filter" property is the one that affect the gradient in Internet Explorer. I tested the example posted above with IE9 on Windows Vista, and it worked in my tests.