Insert
Code:
.tcat2
{
background: #newcolor url(../../images/gradients/new_image.gif) repeat-x top left;
color: #FFFFFF;
font: bold 10pt verdana, geneva, lucida, 'lucida grande', arial, helvetica, sans-serif;
}
Into the Additional CSS Definitions box at the bottom of the Style Manager. Then open up FORUMHOME template and replace all instances of "tcat" with "tcat2".
You might have to change the image path depending on if you have the CSS stored in the filesystem or not.