Prozess-Ablaufdiagramm in TikZ: Nodeform gesucht.

\documentclass[a4paper]{article}
\usepackage[margin=2cm, showframe=false]{geometry}
\usepackage{tikz}
\usetikzlibrary{matrix}
\usetikzlibrary{arrows}
\usetikzlibrary{backgrounds}

\foreach \column/\mycolor in {1/152C47, 2/1C7BB7, 3/0B43AB, 4/5990FF, 5/90ADDF, 6/B2CBE9}{
  \xglobal\definecolor{color\column}{HTML}{\mycolor}
}

\pgfmathsetlengthmacro\spaltenbreite{2.45cm}
\pgfmathsetlengthmacro\HoeheZeileI{1.567cm}
\pgfmathsetlengthmacro\HoeheZeileII{4.25cm}
\pgfmathsetlengthmacro\pfeilhoehe{0.25*\spaltenbreite}

\newcommand\titelI{Titel 1}
\newcommand\textI{1}
\newcommand\titelII{Titel 2}
\newcommand\textII{2}
\newcommand\titelIII{Titel 1}
\newcommand\textIII{3}
\newcommand\titelIV{Titel 1}
\newcommand\textIV{4}
\newcommand\titelV{Titel 5}
\newcommand\textV{Das ist der Text in der zweiten Zeile, in der fünften Spalte.}
\newcommand\titelVI{Titel 6}
\newcommand\textVI{6}

\begin{document}
\begin{tikzpicture}[
  font=\sffamily, 
  >=latex, 
  myshade/.style={
    shade, top color=color#1,  bottom color=color#1!44!white, 
  },
]
  \matrix (m) [matrix of nodes, nodes in empty cells,
    nodes={draw=none, 
      anchor=center, minimum width=\spaltenbreite,
    }, 
    column sep=0mm, row sep=0mm, 
    row 1/.style={minimum height=\HoeheZeileI,
      font=\hspace{1em}\sffamily\bfseries, text=white, 
    }, 
    row 1 column 6/.style={text=black},
    row 2/.style={anchor=north west, 
      text width=\spaltenbreite-1cm, 
      minimum height=\HoeheZeileII, text depth=\spaltenbreite-0.1cm,
    }, 
  ]{
    \titelI  & \titelII & \titelIII  & \titelIV &  \titelV  & \titelVI  \\
    \textI  & \textII & \textIII  & \textIV &  \textV  & \textVI  \\
%    1  &  2 &  3   &  4 &  5    &  6  \\ 
  };

%% Annotationen
  \pgfmathsetmacro\h{0.5*sin(45)}
  \foreach \col in {6,...,1}{
    \begin{scope}[on background layer]
      \path[myshade=\col, draw=white, ultra thick,
        on background layer, 
      ] (m-1-\col.north west) 
        -- (m-1-\col.north east) -- +(\pfeilhoehe,-0.5*\HoeheZeileI) 
        -- (m-1-\col.south east) -- (m-1-\col.south west) --cycle;
    \end{scope}
%
    \path[myshade=\col, draw=none
    ] (m-2-\col.north west) --  (m-2-\col.north east) -- +(-45:0.5) --  ([shift={(-45:0.5)}]m-2-\col.north west) --cycle;
%
    \ifnum\col=6 \else% 
      \draw[gray, dotted, ultra thick
      ] (m-1-\col.south east) -- +(-45:0.5) -- ([xshift=\h cm]m-2-\col.south east); \fi%
  }

  \draw[*->, gray, dotted, ultra thick,
    text width=3cm, 
  ] ([yshift=-0.5cm]m-2-1.south west) -- ([yshift=-0.5cm]m-2-6.south east)
    node[very near start, above]{Text auf Achse}
    node[very near start, below]{Text unter Achse}  
    node[very near end, below]{Text am Ende};

  \draw[ ->, line width=0.333em, color3]  
  (m-1-5.north) -- +(0,1) -- ([yshift=1cm]m-1-4.north) node[midway, above]{Buget überschritten} -- (m-1-4.north);

  \node[anchor=west] at ([yshift=1cm]m-1-1.north west) {Text links oben.};
\end{tikzpicture}
\end{document}