Changing style of alert environment in beamer

Question

I would like to specify a background color in the alert environment. I can, for example, use

\setbeamercolor{alerted text}{fg=blue} 

to change the colour of the alterted text to blue, but this

\setbeamercolor{alerted text}{bg=blue} 

does not work. Is there a way to get around this?

I find that the font colours that the alert environment makes are too subtle and I'd like to add a coloured highlight box around my text in addition to changing the fg colour.

Answer 1

Since (La)TeX doesn't have a “background color” for text, you would have to put your text inside a box which you can then color. Consider the following example using \colorbox.

\documentclass{beamer}

\setbeamercolor{alerted text}{fg=white,bg=red}
\newcommand{\boxalert}[1]{{%
  \usebeamercolor{alerted text}\colorbox{bg}{\alert{#1}}%
}}

\begin{document}
\begin{frame}
Hello \boxalert{World}!
\end{frame}
\end{document}

Which renders

Edit: I'm no expert in beamer internals, so the following is nothing more than a hack. However, if you would like \boxalert to work with overlays, something like the following “seems” to work:

\newenvironment{boxalertenv}{\begin{altenv}%
      {\usebeamertemplate{alerted text begin}\usebeamercolor[fg]{alerted text}\usebeamerfont{alerted text}\colorbox{bg}}
      {\usebeamertemplate{alerted text end}}{\color{.}}{}}{\end{altenv}}

\newcommand<>{\boxalert}[1]{{%
  \begin{boxalertenv}#2{#1}\end{boxalertenv}%
}}

...

Hello \boxalert<2>{World}!