Change colour of italics font for the whole document

Question

I would like to see the following in my latex file: once I use the \textit{...} command, I would like to see that this text does not only get the italics font, but also gets the colour blue. I want to apply this on the whole document. Instead of having to specify it for every part of text that should get this font, is there a way I can specify it in the beginning of the document such that it is applied to the whole doc? Basically I want to change the default properties of the \textit{...} command.

Answer 1

This is very easy with (Xe|Lua)LaTeX:

\documentclass{article}

\usepackage{fontspec}
\usepackage{xcolor}

\setmainfont{Latin Modern Roman}[
  ItalicFeatures={Color=blue},
]

\begin{document}

Some text \emph{emphasized} and \textit{in italic}.

\end{document}

With pdflatex it's a bit more complicated:

\documentclass{article}

\usepackage{xcolor}

\makeatletter
\DeclareRobustCommand{\itshape}{%
  \not@math@alphabet\itshape\mathit
  \fontshape\itdefault\selectfont
  \color{blue}%
}
\makeatother

\begin{document}

Some text \emph{emphasized} and \textit{in italic}.

\end{document}

Be careful of not using \itshape between paragraphs, though.

Answer 2

Here's a command, called \coloremph, which builds on the \emph to allow the emphasized material to be rendered in a color. The default color is blue, but that this may be overridden by providing a different color in the optional argument of \coloremph.

With this setup, any "inner" emphasized material will be rendered in the upright font shape, but with the color of the surrounding emphasized material. Uncomment the directive

%\renewcommand\eminnershape{\upshape\color{black}} % optional

if you want the inner emphasized material to be typeset in black.

Here's the full MWE (minimum working example):

\documentclass{article}
\usepackage[dvipsnames,svgnames,x11names]{xcolor} % for lots of predefined color names
\newcommand\coloremph[2][blue]{\textcolor{#1}{\emph{#2}}}
%\renewcommand\eminnershape{\upshape\color{black}} % optional

\begin{document}
Hello, World.

\coloremph{Once upon a \emph{very strange} time, \dots}

\coloremph[Coral3]{Once upon a \emph{very strange} time, \dots}

\coloremph[MediumPurple]{Once upon a \emph{very strange} time, \dots}

Hello World.
\end{document}