Add system colour change handler to wxSashWindow

Closes #26638.

include/wx/generic/sashwin.h

@@ -157,6 +157,7 @@ public:
 
 private:
     void Init();
+    void OnSysColourChanged(wxSysColourChangedEvent& event);
 
     wxSashEdge  m_sashes[4];
     int         m_dragMode;

src/generic/sashwin.cpp

@@ -38,6 +38,7 @@ wxIMPLEMENT_DYNAMIC_CLASS(wxSashEvent, wxCommandEvent);
 wxBEGIN_EVENT_TABLE(wxSashWindow, wxWindow)
     EVT_PAINT(wxSashWindow::OnPaint)
     EVT_SIZE(wxSashWindow::OnSize)
+    EVT_SYS_COLOUR_CHANGED(wxSashWindow::OnSysColourChanged)
     EVT_MOUSE_EVENTS(wxSashWindow::OnMouseEvent)
 #if defined( __WXMSW__ ) || defined( __WXMAC__)
     EVT_SET_CURSOR(wxSashWindow::OnSetCursor)
@@ -76,7 +77,6 @@ void wxSashWindow::Init()
     m_mouseCaptured = false;
     m_currentCursor = nullptr;
 
-    // Eventually, we'll respond to colour change messages
     InitColours();
 }
 
@@ -359,6 +359,12 @@ void wxSashWindow::OnSize(wxSizeEvent& WXUNUSED(event))
     SizeWindows();
 }
 
+void wxSashWindow::OnSysColourChanged(wxSysColourChangedEvent& event)
+{
+    InitColours();
+    event.Skip();
+}
+
 wxSashEdgePosition wxSashWindow::SashHitTest(int x, int y, int WXUNUSED(tolerance))
 {
     int cx, cy;