How do i change the background color of a window

Hi,
I am unable to change the background color of my window.
How do i change it?
Please help me to do this.

void CTry::OnPaint()
{
CPaintDC dc(this);

CRect rect;
GetClientRect(rect);
CBrush m_Brush(RGB(155,200,155));
dc.FillRect(rect,&m_Brush);

}


}

XingXing