Highlight punctuation marks in pdf

Question

I would like to automatically highlight all punctuation in my document, ideally with a different background color, or by changing the color of the punctuation mark.

The aim is mostly for me to cross check my sentence length aand general style, so I'm not worried about dots in equations and/or headlines.

Is there an easy way for me to 'redefine' a dot as \color{red}{.} to turns all dots red?

Solution using the accepted answer below (because I can't make code work in the comments)

\usepackage{xcolor}
\usepackage{stringstrings}

\let\svcomma,\let\svperiod.\let\svsemicolon;
\catcode`,=\active\catcode`.=\active \catcode`;=\active %
\newcommand\colorpuncton[1][red]{%
% \catcode`,=\active\def,{\colorbox{#1}{\svcomma}}%
  \catcode`.=\active\def.{\colorbox{blue!30}{\svperiod}}%
  \catcode`;=\active\def;{\colorbox{green!30}{\svsemicolon}}%
}

\def\colorpunctoff{%
\catcode`,=12\let ,\svcomma%
\catcode`.=12\let .\svperiod%
\catcode`;=12\let ;\svperiod%
 }

\catcode`,=12 \catcode`.=12 \catcode`;=12 %

\parskip 1em

\let\oldfigure\figure% Store old figure environment start
\let\endoldfigure\endfigure% Store old figure environment end
\renewenvironment{figure}[1][htbp]% Redefine figure
 {\colorpunctoff\oldfigure[#1]}
 {\endoldfigure\colorpuncton}
\let\oldtable\table% 
\let\endoldtable\endtable% 
\renewenvironment{table}[1][htbp]% 
 {\colorpunctoff\oldtable[#1]}
 {\endoldtable\colorpuncton}

 \let\oldSI\SI
 \renewcommand{\SI}[2]{\colorpunctoff\oldSI{#1}{#2}\colorpuncton}

Answer 1

Based on my answer at Change the color of capital letters. The ability to turn it off might allow things like the period to be used in the normal way when needed.

EDITED to allow simple suspend/renew of the method, if one must call on some other macro requiring punctuation, such as \cite. RE-EDITED to allow this suspend/renew in a single macro call, \Xcite{}.

\documentclass{article}
\usepackage{xcolor}
\usepackage{stringstrings}

\let\svcomma,\let\svperiod.\let\svsemicolon;
\catcode`,=\active \catcode`.=\active \catcode`;=\active %
\newcommand\colorpunctinit[1][red]{\colorpuncton%
  \def,{\colorbox{#1}{\svcomma}}%
  \def.{\colorbox{#1}{\svperiod}}%
  \def;{\colorbox{#1}{\svsemicolon}}%
}
\newcommand\colorpuncton{%
  \catcode`,=\active %
  \catcode`.=\active %
  \catcode`;=\active %
}
\def\colorpunctoff{%
  \catcode`,=12 %
  \catcode`.=12 %
  \catcode`;=12 %
}
\newcommand\coloron[2]{%
  \if\svcomma#1\catcode`,=\active\def,{\colorbox{#2}{\svcomma}}\else%
  \if\svperiod#1\catcode`.=\active\def.{\colorbox{#2}{\svperiod}}\else%
  \if\svsemicolon#1\catcode`;=\active\def;{\colorbox{#2}{\svsemicolon}}\else%
\fi\fi\fi%
}
\newcommand\coloroff[1]{\catcode`#1=12%
  \edef\tmp{\detokenize{#1}}%
  \caselower[q]{\tmp}%
  \expandafter\let\expandafter#1\csname sv\thestring\endcsname%
}
\catcode`,=12 \catcode`.=12 \catcode`;=12 %

\parskip 1em

\newcommand\Xcite{\colorpunctoff\citeX}
\newcommand\citeX[1]{\cite{#1}\colorpuncton}

\begin{document}
\colorpunctinit[cyan]
\verb|\colorpunctinit[color]| will change all punctuation to the specified color,\\
here cyan, and should be done to initialize this process.\\
(\verb|But not commas; for some reason, in \verbatim.|)

\colorpunctoff
\verb|\colorpunctoff| will, indeed, suspend the procedure.

\coloron{,}{red}\coloron{.}{blue!30}\coloron{;}{green!30}
\verb|\coloron{<punctuation>}{color}| will turn an inactive symbol active with the
specified color, done here  with red, to ",", blue!30 to the ``.'' and green!30 to the
``;''.

\coloroff{,}
\verb|\coloroff{<punctuation>}|, done here to the comma,
will restore that letter to the original LaTeX
setting; the others remain active.

\coloron{,}{cyan!40}
To change the color an already active symbol, one must first turn the color off;
then set the color anew, as done here to the comma ``,''.

To use \verb|\cite|, one must employ \verb|\Xcite{A, B}|
as in \Xcite{A, B}. The punctuation, it is still colored; yes it is.
\end{document}

Answer 2

You can make the period active and give it a definition. But you should be aware that periods are quite often part of the syntax e.g. of numbers, and that you can get quite horrible errors if the period is not what the syntax expects. So you will have to change the catcode again in such cases.

\documentclass{article}
\usepackage{xcolor}
\usepackage{tikz}
\begin{document}
\catcode`\.=13
\def.{\colorbox{red}{\string.}}

a horse. a horse. a horse.

\catcode`\.=12 %disable the colored period
\begin{tikzpicture}
\draw(0.5,0.5)--(1,1);
\end{tikzpicture}
\catcode`\.=13

a kingdom.

\end{document}