combox只能用dropdownlist的情况下，怎样才能显示我定义的背景色呢？

void CObjFieldCombox::InitObj
{
......

//DWORD dwStyle = CBS_AUTOHSCROLL|CBS_DROPDOWNLIST|WS_VSCROLL|WS_CHILD|WS_CLIPCHILDREN|WS_CLIPSIBLINGS|WS_TABSTOP|WS_VISIBLE|WS_BORDER;
   DWORD dwStyle = CBS_AUTOHSCROLL|CBS_DROPDOWN|WS_VSCROLL|WS_CHILD|WS_CLIPCHILDREN|WS_CLIPSIBLINGS|WS_TABSTOP|WS_VISIBLE|WS_BORDER;

GetWnd()->Create(dwStyle, rc, m_pPage->m_pWnd, ID_OBJINIT + nTabIndex);

GetWnd()->GetWindowRect(&m_rcOrgSite);
m_pPage->m_pWnd->ScreenToClient(&m_rcOrgSite);

......
}