[Tex/LaTex] ! Package xcolor Error: Undefined color model `blue’

Question

I'm having this error message:

! Package xcolor Error: Undefined color model `blue'.

No threads on tex.stackexchange were able to be helpul to me.

I use a modified version of sharelatex.sty template. This is my code:

%==============================================================================
% Beamer style for posters
% // based on 'cpbgposter' beamer theme //
%==============================================================================


\ProvidesPackage{beamerthemesharelatex}


\RequirePackage{tikz}
\usetikzlibrary{arrows,decorations.pathmorphing,backgrounds,calc}
\RequirePackage[T1]{fontenc}
\RequirePackage{lmodern}
\RequirePackage{textcomp}
\RequirePackage{amsmath,amssymb}
\usefonttheme{professionalfonts}

\usepackage{ragged2e}

% normal math font
%\usepackage{mathptmx}
% funny math font
\usepackage{euler}

%%% other text fonts
%\usepackage{palatino}
%\usepackage{bookman}
%\usepackage{utopia}
%\usepackage{tgpagella}
%\usepackage{tgheros}
%
%\renewcommand\rmdefault{qtm}
%\renewcommand\sfdefault{qhv}
%\renewcommand\ttdefault{qcr}
\renewcommand\ttdefault{lmvtt}

% multicols
\usepackage{multicol}
\setlength{\columnsep}{80pt}

% captions
\usepackage[justification=justified,listformat=simple,format=plain,labelformat=simple]{caption}

\usepackage{url}

%\usepackage{xcolor}
\usepackage{pgf}
\usepackage{pgfpages}
\pgfpagesdeclarelayout{boxed}
{
  \edef\pgfpageoptionborder{0pt}
}
{
  \pgfpagesphysicalpageoptions
  {%
    logical pages=1,%
  }
  \pgfpageslogicalpageoptions{1}
  {
    border code=\color[blue]{0.4}\pgfsetlinewidth{20pt}\pgfstroke,%
    border shrink=\pgfpageoptionborder,%
    resized width=.98\pgfphysicalwidth,%
    resized height=.98\pgfphysicalheight,%
    center=\pgfpoint{.5\pgfphysicalwidth}{.5\pgfphysicalheight}%
  }%
}

\pgfpagesuselayout{boxed}
%==============================================================================
% define basic colors 
%==============================================================================
%==============================================================================

  \definecolor{color0}  {RGB}{0,0,0} %%% text color
  \definecolor{color1}  {RGB}{20,66,129} %%% title and subsection color
  \definecolor{color2}  {RGB}{28,130,185} %%% section color
  \definecolor{color3}  {RGB}{255,253,250} %%% background color

%==============================================================================
%==============================================================================

%set the basic colors palette
%   \setbeamercolor{palette primary}   {fg=color0,bg=color3}
%   \setbeamercolor{palette secondary} {fg=color0,bg=color3}
%   \setbeamercolor{palette tertiary}  {fg=color0,bg=color3}
%   \setbeamercolor{palette quaternary}{fg=color0,bg=color3}
  \setbeamercolor{structure}{fg=color1}
%   \setbeamercolor{titlelike}         {bg=color1,fg=color3}
%   \setbeamercolor{frametitle}        {bg=color2!10,fg=color2}
%
  \setbeamercolor{colorbar}{fg=color0,bg=color1}
  \setbeamercolor{normal text}{fg=color0}

% background color
  \beamertemplatesolidbackgroundcolor{color3}
  %\beamertemplateshadingbackground{color3}{color3!70!color1}

%set the fonts
  \setbeamerfont{section in head/foot}{series=\bfseries}
  \setbeamerfont{block title}{series=\bfseries}
  \setbeamerfont{block alerted title}{series=\bfseries}
  \setbeamerfont{frametitle}{series=\bfseries}
  \setbeamerfont{frametitle}{size=\Large}
  \setbeamerfont{caption}{size=\normalsize}
  \setbeamerfont{caption name}{size=\normalsize}

%set some beamer theme options
  \setbeamertemplate{title page}[default][colsep=-4bp,rounded=true]
  \setbeamertemplate{sections/subsections in toc}[square]
  \setbeamertemplate{items}[circle]
  \setbeamertemplate{blocks}[width=0.0]
  \beamertemplatenavigationsymbolsempty
%set bibliography style
 \setbeamertemplate{bibliography item}[text]
 \setbeamercolor{bibliography item}{fg=color0,bg=color3}
 \setbeamercolor{bibliography entry author}{fg=color0,bg=color3}
 \setbeamerfont{bibliography item}{size=\small}
 \setbeamerfont{bibliography entry author}{size=\small}


%
%==============================================================================
% build the poster title
%==============================================================================
\setbeamertemplate{headline}{
 \leavevmode
  \begin{columns}
   \begin{column}{0.15\linewidth}
    \begin{center}
     \includegraphics[width=1\linewidth]{images/ericae}
    \end{center}
   \end{column}
   \begin{column}{.7\linewidth}
    \vskip2cm
    \centering
    %\usebeamercolor{title in headline}
{\color{color2} \textbf{\huge{\inserttitle}}\\[1ex]}
    \vskip 1.5cm
    %\usebeamercolor{author in headline}
{\color{fg} \Large{\insertauthor}\\[1ex]}
    %\usebeamercolor{institute in headline}
{\color{fg} \large{\insertinstitute}\\[1ex]}
        \vskip2cm
      \end{column}
       \begin{column}{.15\linewidth}
         \begin{center}
           \includegraphics[width=1\linewidth]{images/ulaval}
         \end{center}
       \end{column}
        \vspace{1cm}
    \end{columns}

%%% additional bar under titles
%\begin{beamercolorbox}[colsep=0.5cm]{colorbar}
%\end{beamercolorbox}
}


%==============================================================================
% build the poster foot
%==============================================================================
\setbeamertemplate{footline}{
 \leavevmode
    \vskip2cm
  \begin{center}
\begin{minipage}[c][3cm][c]{0.95\textwidth}
  \begin{center}
%
     \begin{flushleft}
     \vskip-1cm
     \begin{tikzpicture}[
remember picture,overlay,
%background rectangle/.style={fill=color3},show background rectangle
]
       \shade [inner color=color2,outer color=color3] (0,0) rectangle (\textwidth,0.3cm);
     \end{tikzpicture}
     \end{flushleft}
%
  \vskip1cm
    \centering
    %\usebeamercolor{title in headline}
{\color{fg} \textbf{\large{\insertshorttitle}}}
%
  \end{center}
\end{minipage}
  \end{center}
    \vskip1cm
}

%
%==============================================================================
% Section and subsection re-definitions

\renewcommand{\section}[1]{
\par\vskip\medskipamount%
%
     \begin{flushleft}
     \begin{tikzpicture}[remember picture,overlay]
       \shade [inner color=color2,outer color=color3] (0,0) rectangle (\columnwidth,0.3cm);
     \end{tikzpicture}
     \end{flushleft}
%
     \begin{center}
     %\vskip1cm
     {\textcolor{color2}{\textbf{\Large #1}}}
     {\parskip0pt\par}
     \end{center}
%
     \begin{flushleft}
     \vskip-1cm
     \begin{tikzpicture}[remember picture,overlay]
       \shade [inner color=color2,outer color=color3] (0,0) rectangle (\columnwidth,0.3cm);
     \end{tikzpicture}
     \end{flushleft}
%
  {\parskip0pt\par}
  \justifying
}

%%%
\renewcommand{\subsection}[1]{
\par\vskip\medskipamount%
     \begin{center}
     \vskip0.8cm
     {\textcolor{color1}{\textbf{\textsl{\large #1}}}}
     {\parskip0pt\par}
     \end{center}
%
  \justifying
}

%==============================================================================

Below is the poster.tex code:

    \documentclass[final]{beamer}
\usepackage[orientation=portrait,size=a0,
            scale=1.25         % font scale factor
           ]{beamerposter}

\geometry{
  hmargin=2.5cm, % little modification of margins
}

%
\usepackage[utf8]{inputenc}

\linespread{1.15}
%
%==The poster style============================================================
\usetheme{sharelatex}

%==Title, date and authors of the poster=======================================
\title
[Journée de la recherche de la Faculté des Sciences et de Génie de l'Université Laval, 12 mars 2014] % Conference
{ % Poster title
Réingénierie des logiciels d'enseignement à distance à l'aide de techniques d'ingénierie de connaissance %\ldots{}
}

\author{ % Authors
Tonguim Ferdinand GUINKO, Laurence CAPUS
}
\institute
[Very Large University] % General University
{
\{tonguim-ferdinand.guinko.1, laurence.capus\}@ulaval.ca \\[0.3ex]
Laboratoire ERICAE\\[0.3ex]
Département d'informatique et genie logiciel\\[0.3ex]
Université Laval
}
\date{\today}



\begin{document}
\begin{frame}[t]

Answer 1

border code=\color[blue]{0.4}\pgfsetlinewidth{20pt}\pgfstroke,%

I suppose you meant color model gray \color[gray]{0.4} or maybe \color{blue!40}