[projects] Add signals for background color and selection color change

python/core/auto_generated/qgsproject.sip.in

@@ -1412,6 +1412,24 @@ Emitted whenever the project's color scheme has been changed.
 .. versionadded:: 3.6
 %End
 
+    void backgroundColorChanged();
+%Docstring
+Emitted whenever the project's canvas background color has been changed.
+
+.. seealso:: :py:func:`setBackgroundColor`
+
+.. versionadded:: 3.10
+%End
+
+    void selectionColorChanged();
+%Docstring
+Emitted whenever the project's selection color has been changed.
+
+.. seealso:: :py:func:`setSelectionColor`
+
+.. versionadded:: 3.10
+%End
+
 
     void layersWillBeRemoved( const QStringList &layerIds );
 %Docstring

src/core/qgsproject.cpp

@@ -3206,6 +3206,8 @@ void QgsProject::setBackgroundColor( const QColor &color )
   writeEntry( QStringLiteral( "Gui" ), QStringLiteral( "/CanvasColorRedPart" ), color.red() );
   writeEntry( QStringLiteral( "Gui" ), QStringLiteral( "/CanvasColorGreenPart" ), color.green() );
   writeEntry( QStringLiteral( "Gui" ), QStringLiteral( "/CanvasColorBluePart" ), color.blue() );
+
+  emit backgroundColorChanged();
 }
 
 QColor QgsProject::backgroundColor() const
@@ -3221,6 +3223,8 @@ void QgsProject::setSelectionColor( const QColor &color )
   writeEntry( QStringLiteral( "Gui" ), QStringLiteral( "/SelectionColorGreenPart" ), color.green() );
   writeEntry( QStringLiteral( "Gui" ), QStringLiteral( "/SelectionColorBluePart" ), color.blue() );
   writeEntry( QStringLiteral( "Gui" ), QStringLiteral( "/SelectionColorAlphaPart" ), color.alpha() );
+
+  emit selectionColorChanged();
 }
 
 QColor QgsProject::selectionColor() const

src/core/qgsproject.h

@@ -1421,6 +1421,22 @@ class CORE_EXPORT QgsProject : public QObject, public QgsExpressionContextGenera
      */
     void projectColorsChanged();
 
+    /**
+     * Emitted whenever the project's canvas background color has been changed.
+
+     * \see setBackgroundColor()
+     * \since QGIS 3.10
+     */
+    void backgroundColorChanged();
+
+    /**
+     * Emitted whenever the project's selection color has been changed.
+
+     * \see setSelectionColor()
+     * \since QGIS 3.10
+     */
+    void selectionColorChanged();
+
     //
     // signals from QgsMapLayerRegistry
     //

tests/src/python/test_qgsproject.py

@@ -1242,7 +1242,9 @@ class TestQgsProject(unittest.TestCase):
         blue = int(s.value("qgis/default_canvas_color_blue", 255))
         # test default canvas backgroud color
         self.assertEqual(p.backgroundColor(), QColor(red, green, blue))
+        spy = QSignalSpy(p.backgroundColorChanged)
         p.setBackgroundColor(QColor(0, 0, 0))
+        self.assertEqual(len(spy), 1)
         # test customized canvas background color
         self.assertEqual(p.backgroundColor(), QColor(0, 0, 0))
 
@@ -1256,7 +1258,9 @@ class TestQgsProject(unittest.TestCase):
         alpha = int(s.value("qgis/default_selection_color_alpha", 255))
         # test default feature selection color
         self.assertEqual(p.selectionColor(), QColor(red, green, blue, alpha))
+        spy = QSignalSpy(p.selectionColorChanged)
         p.setSelectionColor(QColor(0, 0, 0, 50))
+        self.assertEqual(len(spy), 1)
         # test customized feature selection color
         self.assertEqual(p.selectionColor(), QColor(0, 0, 0, 50))