Initializing the Dialog Box
After the dialog box and all of its controls are created but just before the dialog box (of either type) appears on the screen, the dialog object's OnInitDialog member function is called. For a modal dialog box, this occurs during the DoModal call. For a modeless dialog box, OnInitDialog is called when Create is called. You typically override OnInitDialog to initialize the dialog box's controls, such as setting the initial text of an edit box. You must call the OnInitDialog member function of the base class, CDialog, from your OnInitDialog override.
If you want to set your dialog box's background color (and that of all other dialog boxes in your application), see Setting the Dialog Box's Background Color.