Fix updating compare dialog color scheme when switching between dark and light modes w/out a Studio restart. (fixes #9225 )

Author: mpaperno

src/slic3r/GUI/MainFrame.cpp

@@ -2531,6 +2531,9 @@ void MainFrame::on_sys_color_changed()
 
     MenuFactory::sys_color_changed(m_menubar);
 
+    // update DiffPresetDialog from here, we're friends
+    diff_dialog.on_sys_color_changed();
+
     WebView::RecreateAll();
 
     this->Refresh();

src/slic3r/GUI/UnsavedChangesDialog.hpp

@@ -454,6 +454,8 @@ class DiffPresetDialog : public DPIDialog
 protected:
     void on_dpi_changed(const wxRect& suggested_rect) override;
     void on_sys_color_changed() override;
+
+    friend class MainFrame;  // for on_sys_color_changed()
 };
 
 }