diff --git a/resources/celerity/map.php b/resources/celerity/map.php
--- a/resources/celerity/map.php
+++ b/resources/celerity/map.php
@@ -117,7 +117,7 @@
     'rsrc/css/layout/phabricator-source-code-view.css' => 'cbeef983',
     'rsrc/css/phui/calendar/phui-calendar-day.css' => 'f15bb6d6',
     'rsrc/css/phui/calendar/phui-calendar-list.css' => '5d89cd71',
-    'rsrc/css/phui/calendar/phui-calendar-month.css' => '31cec731',
+    'rsrc/css/phui/calendar/phui-calendar-month.css' => '8e10e92c',
     'rsrc/css/phui/calendar/phui-calendar.css' => 'daadaf39',
     'rsrc/css/phui/phui-action-list.css' => 'c5eba19d',
     'rsrc/css/phui/phui-action-panel.css' => '91c7b835',
@@ -830,7 +830,7 @@
     'phui-calendar-css' => 'daadaf39',
     'phui-calendar-day-css' => 'f15bb6d6',
     'phui-calendar-list-css' => '5d89cd71',
-    'phui-calendar-month-css' => '31cec731',
+    'phui-calendar-month-css' => '8e10e92c',
     'phui-chart-css' => '6bf6f78e',
     'phui-crumbs-view-css' => 'b4fa5755',
     'phui-curtain-view-css' => '7148ae25',
diff --git a/src/view/phui/calendar/PHUICalendarMonthView.php b/src/view/phui/calendar/PHUICalendarMonthView.php
--- a/src/view/phui/calendar/PHUICalendarMonthView.php
+++ b/src/view/phui/calendar/PHUICalendarMonthView.php
@@ -65,7 +65,6 @@
     foreach ($days as $day) {
       $day_number = $day->format('j');
 
-      $class = 'phui-calendar-month-day';
       $weekday = $day->format('w');
 
       $day->setTime(0, 0, 0);
@@ -115,13 +114,20 @@
 
       $day_id = $day->format('Ymd');
 
+
+      $classes = array();
+      if ($day->format('m') != $this->month) {
+        $classes[] = 'phui-calendar-month-adjacent';
+      }
+      $classes = implode(' ', $classes);
+
       $cell_lists[$day_id] = array(
         'dayID' => $day_id,
         'list' => $list,
         'date' => $day,
         'dayURI' => $uri,
         'count' => count($all_day_events) + count($list_events),
-        'class' => $class,
+        'class' => $classes,
       );
     }
 
@@ -219,6 +225,7 @@
 
     $classes = array();
     $classes[] = 'phui-calendar-month-event-list';
+    $classes[] = 'phui-calendar-month-day';
     $classes[] = $event_list['class'];
     $classes = implode(' ', $classes);
 
@@ -285,6 +292,7 @@
 
     $classes = array();
     $classes[] = 'phui-calendar-month-number';
+    $classes[] = $event_list['class'];
 
     if ($date) {
       if ($this->isDateInCurrentWeek($date)) {
diff --git a/webroot/rsrc/css/phui/calendar/phui-calendar-month.css b/webroot/rsrc/css/phui/calendar/phui-calendar-month.css
--- a/webroot/rsrc/css/phui/calendar/phui-calendar-month.css
+++ b/webroot/rsrc/css/phui/calendar/phui-calendar-month.css
@@ -222,3 +222,7 @@
 .device-desktop td.phui-calendar-month-number.calendar-hover {
   background: {$lightblue};
 }
+
+.phui-calendar-month-adjacent {
+  background: {$greybackground};
+}