How to automatically color a string that starts by a specific character (@)?

Question

Using the memoir class, I'm looking for a way to automatically color any string that starts whith an @ character, whether it be in the main text or in a footnote. Any idea how to do that?

Update : I also use bibtex, and i don't want link box or color to my citation, that explain the hidelink option.

With a minimal example :

\documentclass[a4paper, 12pt,twoside, openright]{memoir}
\usepackage{polyglossia}
\setdefaultlanguage{french}
\usepackage{fontspec}
\usepackage[usenames,dvipsnames]{xcolor}
\usepackage[autostyle=true,french=guillemets,maxlevel=3]{csquotes}
\usepackage{xparse}
\usepackage{graphicx}
\usepackage[protrusion=true]{microtype}

\makeatletter

\renewcommand\@makefnmark{\hbox{\@textsuperscript{\normalfont\color{BurntOrange}\@thefnmark}}}
\renewcommand\@makefntext[1]{%
  \parindent 1em\noindent
            \hb@xt@1.8em{%
                \hss\@textsuperscript{\normalfont\@thefnmark}}#1}
\makeatother

\usepackage[hidelinks, pdfusetitle]{hyperref} % Creates hyperlinks and index in the PDF document, preferably load after biblatex

\begin{document}

\chapterstyle{bringhurst}

This is a link in a footnote \footnote{My link is \href{http://www.google.fr}{@google}}

This is a colored link in my text \href{http://www.google.fr}{@google}

This is a normal link \href{http://www.google.fr}{google}

\end{document}

I want to autodetect and color text link which start with @ and not all the link.

Answer 1

REVISION with general solution to problem of coloring all words beginning with a particular symbol, @. RE-EDITED to handle situation of lone @ character. It is done by making @ active, and then defining it to turn on red and print the saved copy of @. The key to this revision is the macro \tilblank that uses recursion to print out the next word (still in red). When it encounters a space, it reverts to black. If it encounters an end-of-group, it exits (and also reverts to black).

\documentclass{article}
\usepackage{ifnextok}
\usepackage{xcolor}
\makeatletter
\def\tilblank#1{#1\IfNextToken\@sptoken{ \color{black}}{%
  \IfNextToken\egroup{}{\tilblank}}}
\def\atend{\IfNextToken\@sptoken{ \color{black}}\tilblank}
\let\svat @
\makeatother
\catcode`@=\active
\def@{\color{red}\svat\atend}
\begin{document}
This tests @the use of @midstream or in its own {@group}.
Also testing @ by itself and at the end of a @paragraph.

This follows in black, as @it should. 
\end{document}

---

ORIGINAL SOLUTION

I'm not sure if this approach breaks anything else. I make @ active. Also, this only works because your @ words are in their own group. That means if you wanted to use @ in text, it would have to be enclosed in {}.

\documentclass[a4paper, 12pt,twoside, openright]{memoir}
\usepackage{polyglossia}
\setdefaultlanguage{french}
\usepackage{fontspec}
\usepackage[usenames,dvipsnames]{xcolor}
\usepackage[autostyle=true,french=guillemets,maxlevel=3]{csquotes}
\usepackage{xparse}
\usepackage{graphicx}
\usepackage[protrusion=true]{microtype}


\makeatletter

\renewcommand\@makefnmark{\hbox{\@textsuperscript{\normalfont\color{BurntOrange}\@thefnmark}}}
\renewcommand\@makefntext[1]{%
  \parindent 1em\noindent
            \hb@xt@1.8em{%
                \hss\@textsuperscript{\normalfont\@thefnmark}}#1}
\makeatother

\usepackage[hidelinks, pdfusetitle]{hyperref} % Creates hyperlinks and index in the PDF document, preferably load after biblatex

\begin{document}
\let\svat @
\catcode`@=\active
\def@{\color{red}\svat}


\chapterstyle{bringhurst}

This is a link in a footnote \footnote{My link is \href{http://www.google.fr}{@google} checking revert}

This is a colored link in my text \href{http://www.google.fr}{@google}

This is a normal link \href{http://www.google.fr}{google}

\end{document}

\documentclass{article}
\usepackage{xcolor}
\let\svat @
\catcode`@=\active
\def@{\textcolor{red}{\svat}}
\begin{document}
xy@z
\end{document}