Author: Jonas Bilinkevicius

A config form allows the user to change the background, but I can't refresh the 
complete client area when coming back from the config form. Only the config form 
area is refreshed.

Answer:

1   procedure TMainWin.InvalidateClient;
2   var
3     R: TRect;
4   begin
5     R := Classes.Rect(0, 0, ClientWidth, ClientHeight);
6     InvalidateRect(ClientHandle, @R, true);
7   end;