Index: src/kmessagewidget.cpp
===================================================================
--- src/kmessagewidget.cpp
+++ src/kmessagewidget.cpp
@@ -28,6 +28,7 @@
 #include <QPainter>
 #include <QShowEvent>
 #include <QTimeLine>
+#include <QTimer>
 #include <QToolButton>
 #include <QStyle>
 
@@ -200,6 +201,8 @@
         break;
     case KMessageWidget::Error:
         bg1.setRgb(218, 68, 83); // values taken from kcolorscheme.cpp (Negative)
+        // #357210: use darker color to improve the visibility of close button.
+        bg1 = bg1.darker(110);
         fg.setRgb(239, 240, 241);
         break;
     }
@@ -343,6 +346,10 @@
 {
     if (event->type() == QEvent::Polish && !d->content->layout()) {
         d->createLayout();
+    } else if (event->type() == QEvent::WindowActivate) {
+        // Widget is visible AND palette() has the Active color group.
+        // We are now ready to update the colors.
+        d->updateColors();
     }
     return QFrame::event(event);
 }
@@ -401,6 +408,7 @@
 void KMessageWidget::setCloseButtonVisible(bool show)
 {
     d->closeButton->setVisible(show);
+    d->updateColors();
     updateGeometry();
 }