Why is this not working:

\documentclass[a4paper,10pt]{article}
\usepackage{a4wide}
\usepackage[T1]{fontenc}
\usepackage[portuguese]{babel}
\usepackage[latin1]{inputenc}
\usepackage{indentfirst}
\usepackage{listings}
\usepackage{fancyhdr}
\usepackage{url}
\usepackage[compat2,a4paper,left=25mm,right=25mm,bottom=15mm,top=20mm]{geometry}
\usepackage{color}
\usepackage[colorlinks]{hyperref}
\usepackage[pdftex]{graphicx}

\renewcommand{\headrulewidth}{0.4pt}
\renewcommand{\footrulewidth}{0.4pt}

\pagestyle{fancy}

\fancyhead[L]{\small Laboratórios de Informática III}
\fancyhead[R]{\small Projecto 1 (Linguagem \textsf{C})}

\lstset{
    basicstyle=\ttfamily\footnotesize,
    showstringspaces=false,
    frame=single,
    tabsize=4,
    breaklines=true,

}

\definecolor{Section1}{rgb}{0.09,0.21,0.36}
\definecolor{Section2}{rgb}{0.21,0.37,0.56}
\definecolor{Section3}{rgb}{0.30,0.50,0.74}

\hypersetup{
    bookmarks=false,
    linkcolor=red,
    urlcolor=cyan,
}

\renewcommand{\section}[1]{\texorpdfstring{\color{green}#1}{#1}}

\parskip=6pt

\begin{document}

\begin{titlepage}

\begin{center}

\includegraphics[width=5cm]{./logo.jpg}\\[1cm]

\textsc{\LARGE Universidade do Minho}\\[1cm]

\textsc{\large Licenciatura em Engenharia Informática\\Laboratórios de Informática III}\\[1.5cm]

\rule{\linewidth}{0.5mm}\\[0.4cm]

\huge{\textbf{\textsc{Relatório do Projecto 1 (Linguagem C)}}}

\rule{\linewidth}{0.5mm}

\vfill

\begin{tabular}{c c}

    \includegraphics[width=3.5cm]{./nuno.jpg} & \includegraphics[width=3.5cm]{./ricardo.jpg} \\

    \textsc{\large{Nuno Mendes (51161)}} & \textsc{\large{Ricardo Amaral (48404)}} \\

\end{tabular}

\vfill

\large{\today}

\end{center}

\end{titlepage}

\tableofcontents

\newpage

\section{Introdução}

Lorem ipsum...

\newpage

\appendix

\section{\color{Section1}Diagrama das Estruturas de Dados}

\begin{center}
\includegraphics[width=16cm]{./Diagrama.pdf}
\end{center}

\end{document}

! LaTeX Error: Something's wrong--perhaps a missing \item.

See the LaTeX manual or LaTeX Companion for explanation. Type H for immediate help. ...

                                               l.2 ...rline {1}\color

{green}Teste}{3}{section.1}

How can I make it work properly?