Index: wp-includes/general-template.php
===================================================================
--- wp-includes/general-template.php	(revision 15432)
+++ wp-includes/general-template.php	(working copy)
@@ -1190,7 +1190,12 @@
 	} else {
 		$daywithpost = array();
 	}
-
+	
+	if ( is_single() && 1 == count($posts)) 
+		$current_post_day = mysql2date("j m",$posts[0]->post_date);
+	else
+		$current_post_day = false;
+	
 	if (strpos($_SERVER['HTTP_USER_AGENT'], 'MSIE') !== false || stripos($_SERVER['HTTP_USER_AGENT'], 'camino') !== false || stripos($_SERVER['HTTP_USER_AGENT'], 'safari') !== false)
 		$ak_title_separator = "\n";
 	else
@@ -1230,10 +1235,14 @@
 			$calendar_output .= "\n\t</tr>\n\t<tr>\n\t\t";
 		$newrow = false;
 
+		$this_post_html = '';
+		if ( "$day $thismonth" == $current_post_day )
+			$this_post_html = ' class="this_post"';
+			
 		if ( $day == gmdate('j', current_time('timestamp')) && $thismonth == gmdate('m', current_time('timestamp')) && $thisyear == gmdate('Y', current_time('timestamp')) )
-			$calendar_output .= '<td id="today">';
+			$calendar_output .= '<td id="today"'.$this_post_html.'>';
 		else
-			$calendar_output .= '<td>';
+			$calendar_output .= '<td'.$this_post_html.'>';
 
 		if ( in_array($day, $daywithpost) ) // any posts today?
 				$calendar_output .= '<a href="' . get_day_link($thisyear, $thismonth, $day) . "\" title=\"" . esc_attr($ak_titles_for_day[$day]) . "\">$day</a>";