Styling \Blindtext and \blindtext (aka renewcommand with optional arguments)

Question

I am using blindtext package to draw out how the layout of the document will look like and then swapping the "dummy" parts with real text. Problem is that I would like to give some style to these text blocks to visually differentiate them from already written text.

I used simply:

\let\oldbt\blindtext
\renewcommand{\blindtext}[1]{\textcolor{gray}{\oldbt{}}}

which worked fine until I wanted to add some arguments or use \Blindtext, which internally calls \blindtext with arguments.

I found several possibilities to handle optional arguments using \xparse or \NewDocumentCommand, but none of them was enough descriptive. And I still have some blind believe it must be possible to do using standard \renewcommand. I also believe that this will be useful for more people so I am asking new question.

What is the correct way of styling blindtext, for example adding gray color?

Answer 1

You have to be careful in redefining commands with an optional argument; instead of \let one should use \LetLtxMacro (see When to use \LetLtxMacro?).

\documentclass{article}
\usepackage{blindtext,letltxmacro,xcolor,xparse}
\usepackage{lipsum}% for simulating real text

\LetLtxMacro{\blindtextblindtext}{\blindtext}
\LetLtxMacro{\blindtextBlindtext}{\Blindtext}

\RenewDocumentCommand{\blindtext}{O{\value{blindtext}}}{%
  \begingroup\color{gray}\blindtextblindtext[#1]\endgroup
}
\RenewDocumentCommand{\Blindtext}{O{\value{blindtext}}O{\value{Blindtext}}}{%
  \begingroup\color{gray}\blindtextBlindtext[#1][#2]\endgroup
}

\begin{document}

\lipsum[1]

\blindtext[3]

\lipsum[3]

\Blindtext[2][3]

\lipsum[4]

\end{document}