get_calenderで呼び出したカレンダーの土日や平日などに色ってつけたくなったりしちゃいますよね！？
てことで思い立ったが吉日、つけちゃいましょうか！

以下のコードをfunctions.phpに貼付け！

/*****************カレンダー*****************/

//カレンダー土日クラス
function add_week_class2calendar( $calendar_output ) {
    $week_map = array(
        'mon' => '月曜日',
        'tue' => '火曜日',
        'wed' => '水曜日',
        'thu' => '木曜日',
        'fri' => '金曜日',
        'sat' => '土曜日',
        'sun' => '日曜日',
    );
 
    $regex = '/<th scope="col" title="([^"]+?)"/';
    $num = preg_match_all( $regex, $calendar_output, $m );
 
    if ( $num ) {
        $replace = array();
        for ( $i = 0; $i < $num; $i++ ) {
            $replace[$i] = '<th scope="col" class="' . array_search( $m[1][$i], $week_map ) . '" title="' . $m[1][$i] . '"';
        }
        $calendar_output = str_replace( $m[0], $replace, $calendar_output );
    }
    return $calendar_output;
}
add_filter( 'get_calendar', 'add_week_class2calendar' );
 
function add_week_classes2calendar( $calendar_output ) {
    global $wpdb, $m, $monthnum, $year, $wp_locale, $posts;
 
    if ( isset($_GET['w']) )
        $w = ''.intval($_GET['w']);
 
    // Let's figure out when we are
    if ( !empty($monthnum) && !empty($year) ) {
        $thismonth = ''.zeroise(intval($monthnum), 2);
        $thisyear = ''.intval($year);
    } elseif ( !empty($w) ) {
        // We need to get the month from MySQL
        $thisyear = ''.intval(substr($m, 0, 4));
        $d = (($w - 1) * 7) + 6; //it seems MySQL's weeks disagree with PHP's
        $thismonth = $wpdb->get_var("SELECT DATE_FORMAT((DATE_ADD('{$thisyear}0101', INTERVAL $d DAY) ), '%m')");
    } elseif ( !empty($m) ) {
        $thisyear = ''.intval(substr($m, 0, 4));
        if ( strlen($m) < 6 )
                $thismonth = '01';
        else
                $thismonth = ''.zeroise(intval(substr($m, 4, 2)), 2);
    } else {
        $thisyear = gmdate('Y', current_time('timestamp'));
        $thismonth = gmdate('m', current_time('timestamp'));
    }
 
    $jp_holidays = get_option( 'jp_holidays' );
 
    if ( ( ! $jp_holidays || !isset( $jp_holidays[$thisyear . $thismonth] ) || $jp_holidays[$thisyear . $thismonth]['expire'] < time() ) && $thisyear >= 2000 ) {
        $holiday_api = 'http://www.finds.jp/ws/calendar.php?php&y=' . $thisyear . '&m=' . $thismonth . '&t=h&l=2';
        $ch = curl_init( $holiday_api );
        curl_setopt( $ch, CURLOPT_FAILONERROR, true );
        curl_setopt( $ch, CURLOPT_RETURNTRANSFER, true );
        curl_setopt( $ch, CURLOPT_TIMEOUT, 5 );
        $source = curl_exec( $ch );
        curl_close( $ch );
        if ( $source ) {
            $results = maybe_unserialize( $source );
            if ( isset( $results['status'] ) && $results['status'] == 200 ) {
                if ( ! is_array( $jp_holidays ) ) {
                    $jp_holidays = array();
                }
                $jp_holidays[$thisyear . $thismonth] = array();
                if ( isset( $results['result']['day'] ) ) {
                    foreach ( $results['result']['day'] as $hday ) {
                        $jp_holidays[$thisyear . $thismonth][$hday['mday']] = array( 'type' => $hday['htype'], 'name' => $hday['hname'] );
                    }
                    $jp_holidays[$thisyear . $thismonth]['expire'] = time() + 365 * 24 * 3600;
                }
                update_option( 'jp_holidays', $jp_holidays );
            }
        }
    }
 
    $yar = (int)$thisyear;
    $mon = (int)$thismonth;
    $day = 1;
    $regex = array();
    while( checkdate( $mon, $day, $yar ) ) {
        $classes = array();
        $wday = date( 'w', strtotime( sprintf( '%04d-%02d-%02d', $yar, $mon, $day ) ) );
        switch ( $wday ) {
        case 0 :
            $classes[] = 'sun';
            break;
        case 6 :
            $classes[] = 'sat';
            break;
        default :
        }
        if ( $jp_holidays && is_array( $jp_holidays ) && count( $jp_holidays[$thisyear . $thismonth] ) && isset( $jp_holidays[$thisyear . $thismonth][$day] ) ) {
            $classes[] = 'holiday';
        }
        $class = '';

 
        if ( count( $classes ) ) {
            $class =  ' class="' . implode( ' ', $classes ) . '"';
        }
        if ( $class ) {
            $regex['|<td( id="today")?>((<a href="[^"]+" title="[^"]+">)?' . $day . '(</a>)?)</td>|'] = '<td$1' . $class . '>$2</td>';
        }
        $day++;
    }
 
    $calendar_output = preg_replace( array_keys( $regex ), $regex, $calendar_output );
 
    return $calendar_output;
}
add_filter( 'get_calendar', 'add_week_classes2calendar', 0 );

これでカレンダーで使われているテーブルの列にクラスがつくのでそれをスタイルシートで色付けするだけ！
簡単ですね〜笑
ただこのコード、twentytenで使われているfunctions.phpようで作られているぽいのでだめだった場合はほかの方法を探すか、twentytenのfunctipns.phpを使うことをお勧めします