diff --git a/src/agenda/agenda.cpp b/src/agenda/agenda.cpp
--- a/src/agenda/agenda.cpp
+++ b/src/agenda/agenda.cpp
@@ -1660,23 +1660,20 @@
         }
     }
 
+    // Compute the grid line color for both the hour and half-hour
+    // The grid colors are always computed as a function of the palette's windowText color.
     QPen hourPen;
     QPen halfHourPen;
     
-    if (!d->preferences()->useSystemColor()) {
-        hourPen = d->preferences()->agendaGridBackgroundColor().darker(150);
-        halfHourPen = d->preferences()->agendaGridBackgroundColor().darker(125);
+    const QColor windowTextColor = palette().color(QPalette::WindowText);
+    if (windowTextColor.red() + windowTextColor.green() + windowTextColor.blue() < (256 / 2 * 3)) {
+        // dark grey line
+        hourPen = windowTextColor.lighter(200);
+        halfHourPen = windowTextColor.lighter(500);
     } else {
-        const QColor windowTextColor = palette().color(QPalette::WindowText);
-        if (windowTextColor.red() + windowTextColor.green() + windowTextColor.blue() < (256 / 2 * 3)) {
-            // dark grey line
-            hourPen = windowTextColor.lighter(200);
-            halfHourPen = windowTextColor.lighter(500);
-        } else {
-            // light grey line
-            hourPen = windowTextColor.darker(150);
-            halfHourPen = windowTextColor.darker(200);
-        }
+        // light grey line
+        hourPen = windowTextColor.darker(150);
+        halfHourPen = windowTextColor.darker(200);
     }
     
     dbp.setPen(hourPen);