That text is found in themes/default/gallery2.template.php
Around line 6277
echo '<tr class="titlebg"><td align="center" colspan="', $maxrowlevel, '">';
if ($g_bulk && GetCatPermission($cat,'addpic',true) === true)
echo '<a href="', $scripturl, '?action=gallery;sa=bulk;cat=', $cat, '">' , $txt['gallery_text_bulkadd'], '</a> - ';
if ($g_manage)
echo '<a href="', $scripturl, '?action=gallery;sa=addcat;cat=', $cat, '">', $txt['gallery_text_addsubcat'], '</a> - ';
if ($g_add && GetCatPermission($cat,'addpic',true) === true)
echo '<a href="', $scripturl, '?action=gallery;sa=add;cat=', $cat, '">', $txt['gallery_text_addpicture'], '</a> - ';
if (GetCatPermission($cat,'addvideo',true) === true)
if ($g_video)
echo '<a href="', $scripturl, '?action=gallery;sa=addvideo;cat=', $cat, '">', $txt['gallery_form_addvideo'], '</a> - ';
echo '
<a href="', $scripturl, '?action=gallery">', $txt['gallery_text_returngallery'], '</a></td>
</tr>
</table>
</form><br />';
You will need to change the part class="titlebg"
Try changing titlbg to either catbg or windowbg or windowbg2