setbeamertemplate{frametitle}
        {
            begin{beamercolorbox}[ht=2em,wd=paperwidth]{frametitle}
              {
                bfseriesLargestruthspace{10pt}
                insertframetitlehspace{0pt plus 1filll}insertframenumberhspace{10pt}strut
              }
           vskip+0.7ex%
           setbeamercolor{palette quaternary}{fg=white,bg=mygreen}
           end{beamercolorbox}
        }

begin{frame}
frametitle{Title}
end{frame}