The CM_PAINTBACKGROUND message is provided so that an application can subclass the container control and paint its own background. If the application does not subclass the container control or subclasses the container control and returns FALSE, the container uses the system window color, which is specified by SYSCLR_WINDOW. This color can be changed by using the PP_BACKGROUNDCOLOR or PP_BACKGROUNDCOLORINDEX presentation parameter of the WM_PRESPARAMCHANGED (in Container Controls) message.