Unwanted space between beamer colorboxes

Question

I'm trying to create a beamer theme that has some colored boxes at the very top and bottom of each slide. So far, I have copied the default theme and added an empty beamercolorbox to it. While this works, I get a while line between the border line and the subsequent header box. Where does this line come from and how do I get rid of it?

\documentclass{beamer}

\usetheme{default}

\makeatletter
\setbeamercolor{top/bottom bar}{fg=red,bg=red}
\setbeamercolor{titlelike}{parent=structure,fg=black,bg=green}
\setbeamertemplate{frametitle}
{
  \ifbeamercolorempty[bg]{frametitle}{}{\nointerlineskip}%
  \@tempdima=\textwidth%
  \advance\@tempdima by\beamer@leftmargin%
  \advance\@tempdima by\beamer@rightmargin%
  \begin{beamercolorbox}[ht=1.26mm,dp=0mm,wd=\the\@tempdima,colsep=0mm]{top/bottom bar}% <-- INSERTED THIS
  \end{beamercolorbox}% <-- INSERTED THIS
  \begin{beamercolorbox}[sep=0.3cm,1,wd=\the\@tempdima]{frametitle}
    \usebeamerfont{frametitle}%
    \vbox{}\vskip-1ex%
    \if@tempswa\else\csname beamer@fte1\endcsname\fi%
    \strut\insertframetitle\strut\par%
    {%
      \ifx\insertframesubtitle\@empty%
      \else%
      {\usebeamerfont{framesubtitle}\usebeamercolor[fg]{framesubtitle}\insertframesubtitle\strut\par}%
      \fi
    }%
    \vskip-1ex%
    \if@tempswa\else\vskip-.3cm\fi% set inside beamercolorbox... evil here...
  \end{beamercolorbox}%
}
\makeatother

\begin{document}

\begin{frame}
  \frametitle{Foo Bar}
  \begin{itemize}
    \item Foo
    \item Bar
    \item Baz
  \end{itemize}
\end{frame}

\end{document}

Answer 1

  \end{beamercolorbox}% <-- INSERTED THIS
\nointerlineskip% <-- INSERT THIS AS WELL
  \begin{beamercolorbox}[sep=0.3cm,1,wd=\the\@tempdima]{frametitle}