Find something like this in your postbit_legacy template (the 175 is probably a good thing to look for) and make sure you have the class="alt2" there (or alt1, to make it like the cell next to it):
HTML Code:
<tr valign="top">
<td class="alt2" width="175" style="border: $stylevar[cellspacing]px solid $stylevar[tborder_bgcolor]; border-top: 0px; border-bottom: 0px">