Disable color picker under OSX, due to limitations with QWidget::grab…

…Mouse on that platform

src/gui/qgscolorbutton.cpp

@@ -312,9 +312,14 @@ void QgsColorButton::showContextMenu( QMouseEvent *event )
   QAction* pasteColorAction = new QAction( tr( "Paste color" ), 0 );
   pasteColorAction->setEnabled( false );
   colorContextMenu.addAction( pasteColorAction );
+#ifndef Q_WS_MAC
+  //disabled for OSX, as it is impossible to grab the mouse under OSX
+  //see note for QWidget::grabMouse() re OSX Cocoa
+  //http://qt-project.org/doc/qt-4.8/qwidget.html#grabMouse
   QAction* pickColorAction = new QAction( tr( "Pick color" ), 0 );
   colorContextMenu.addSeparator();
   colorContextMenu.addAction( pickColorAction );
+#endif
 
   QColor clipColor;
   if ( colorFromMimeData( QApplication::clipboard()->mimeData(), clipColor ) )
@@ -333,6 +338,7 @@ void QgsColorButton::showContextMenu( QMouseEvent *event )
     //paste color
     setColor( clipColor );
   }
+#ifndef Q_WS_MAC
   else if ( selectedAction == pickColorAction )
   {
     //pick color
@@ -341,10 +347,11 @@ void QgsColorButton::showContextMenu( QMouseEvent *event )
     grabMouse();
     mPickingColor = true;
   }
+  delete pickColorAction;
+#endif
 
   delete copyColorAction;
   delete pasteColorAction;
-  delete pickColorAction;
 }
 
 void QgsColorButton::setValidColor( const QColor& newColor )