Preparing a beamer poster: how to create a border box?

Question

I am preparing a poster with LaTeX using beamerposter, following the examples of the beamerposter site. In these examples, the title is themed with a background color. I would like to have the title framed in a box with a double border, each border with a different color. The following picture should explain it (zoom of the upper left corner of the poster):

In order to achieve this, I tried with a beamercolorbox or an \fcolorbox, but I could not create a border like above.

  \setlength{\fboxrule}{4pt}
  \setlength{\fboxsep}{1pt}
  \fcolorbox{white}{blue}{
    \colorbox{white}{
      Hello test
    }
  }

How can I create a box with a configurable border? I say configurable because I would like to control its thickness and color.

---

Update I have managed to almost do this with tikz box, a minipage and another box. I think this might be a over-complicated solution. The question remains open since I am still having trouble with the border to the right, it disappears due to the width of the minipage.

\definecolor{ltsiBlue1}{rgb}{0.0,0.4,1.0}
\tikzstyle{titleouterbox} = [draw=ltsiBlue1, fill=white, line width=3pt,
    rectangle, inner sep=3pt, inner ysep=3pt]
\tikzstyle{titleinnerbox} = [draw=white, fill=ltsiBlue1, line width=3pt, 
    text=white, rectangle, inner sep=13pt, inner ysep=13pt]
\begin{tikzpicture}
\node [titleouterbox] (box){%
    \begin{minipage}{1.0\textwidth}
      \begin{tikzpicture}
        \node [titleinnerbox] (box){%
          \begin{minipage}{1.0\textwidth}
            hello test
          \end{minipage}
        };
      \end{tikzpicture}
    \end{minipage}
};
\end{tikzpicture}%

Answer 1

I have finally managed to do this with the double and double distance parameters of a tkiz style:

\definecolor{ltsiBlue1}{rgb}{0.0,0.4,1.0} % #0066ff
\tikzstyle{titlebox} = [draw=white, double=ltsiBlue1, double distance=2pt, 
                        fill=ltsiBlue1, line width=3pt, text=white, rectangle, 
                        inner sep=13pt, inner ysep=13pt]
\begin{tikzpicture}
\node [titlebox] (box){%
  Hello world
};
\end{tkizpicture}

Here is the output, after some heavy butchering of one of the examples of beamerposter