c++ - How to set opacity in QtableWidget cell when setting cell background color -

i trying insert few rows in qtablewidget , setting cell background color follows:

        int rowcount = tablewidget->rowcount();         tablewidget->insertrow(rowcount);         qtablewidgetitem *coloitem = new qtablewidgetitem("");          tablewidget->setitem(rowcount, 0, coloitem);         coloitem->setbackground(qt::globalcolor(i)); //qt::globalcolor(fcolor) 

now want set opacity of cell , how can it. couldnot find related qtablewidget.