Changing color of already printed text

Question

For making a small quiz in class I am working on a presentation in beamer.

I want to change the color of statements to red (wrong statement) or green (right statement) but only after my class answered the question.

I was searching the internet, but only found the color package, where you apparently can only change the text color before it appears.

Can someone point me into the right direction?

Answer 1

beamer provides an overlay specification with most of its macros/environments. It allows you to say (for example) ...\alert<2>{<stuff>}... so that <stuff> prints normally on slides other than number 2. \color itself is overlay aware in the form \color<2->{blue}{<stuff>} that would print <stuff> in blue from slide 2 onward. Alternatively, one can use something like ...{\only<2>{\color{blue}}<stuff>}... which prints <stuff> in blue only on slide 2.

Here's a short example

\documentclass{beamer}% http://ctan.org/pkg/beamer
\begin{document}
\begin{frame}
Some text {\only<2>{\color{blue}}and stuff}.
\end{frame}
\end{document}

Note that beamer already loads xcolor.