You can use the CSS :after
(or :before
) pseudo class.
<col span="3" class="index">
CSS:
.index {
position:relative;
background-color: #ccc;
}
.index:after {
position:absolute;
content: "Index";
top:0px;
left:0px;
color:#000000
}
You can also combine this with UTF-8 characters for any glyph you may want to use for your sort indicator.