made default background colour BTNFACE (so that panels don't have to erase their background explicitly); removed now unneeded SetBackgroundColour() in wxDialog which now has default bg colour and restored one in wxFrame which now has a non default one

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@30564 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/msw/app.cpp

@@ -360,8 +360,8 @@ bool wxApp::RegisterWindowClasses()
     wndclass.hInstance     = wxhInstance;
     wndclass.hCursor       = ::LoadCursor((HINSTANCE)NULL, IDC_ARROW);
 
-    // Register the frame window class.
-    wndclass.hbrBackground = (HBRUSH)(COLOR_APPWORKSPACE + 1);
+    // register the class for all normal windows
+    wndclass.hbrBackground = (HBRUSH)(COLOR_BTNFACE + 1);
     wndclass.lpszClassName = wxCanvasClassName;
     wndclass.style         = styleNormal;