Beamer notes with color overlay

Question

I am having trouble with the overlay system of beamer when using side notes. I have a slide with an overlay specification and I have some notes for each stage of this slide. For example, from the beamer docs:

\documentclass[compress,mathserif]{beamer}
\usepackage{pgfpages}
\usetheme{Frankfurt}
\setbeameroption{show notes}
\setbeameroption{show notes on second screen=right}

\begin{document}
\begin{frame}
  \frametitle{There Is No Largest Prime Number}
  \framesubtitle{The proof uses \textit{reductio ad absurdum}.}
  \begin{theorem}
    There is no largest prime number.
  \end{theorem}
  \begin{proof}
    \begin{enumerate}
    \item<1-| alert@1> Suppose $p$ were the largest prime number.
    \item<2-> Let $q$ be the product of the first $p$ numbers.
    \item<3-> Then $q+1$ is not divisible by any of them.
    \item<1-> Thus $q+1$ is also prime and greater than $p$.\qedhere
    \end{enumerate}
  \end{proof}
  \note<1->{ note one\\ }
  \note<2->{ note 2\\ }
  \note<3->{ note 3\\ }
  \note<4->{ note 4\\ }
\end{frame}
\end{document}\endinput

With this example, notes appear as the overlay advances. What I would like is for the notes to be always visible, but somehow highlighted (e.g. in red) in its corresponding slide. I tried with \note<1-| alert@1>, but this didn't work so it seems that I am misunderstanding something about the overlays.

Answer 1

You can use \alt{}{} to color the notes:

\documentclass[compress,mathserif]{beamer}
\usepackage{pgfpages}
\usetheme{Frankfurt}
\setbeameroption{show notes}
\setbeameroption{show notes on second screen=right}

\newcommand<>{\mynote}[1]{%
    \alt#2{%
        \note{\textcolor{red}{#1}}
    }
    {%
        \note{#1}
    }
}

\begin{document}
\begin{frame}
  \frametitle{There Is No Largest Prime Number}
  \framesubtitle{The proof uses \textit{reductio ad absurdum}.}
  \begin{theorem}
    There is no largest prime number.
  \end{theorem}
  \begin{proof}
    \begin{enumerate}
    \item<1-| alert@1> Suppose $p$ were the largest prime number.
    \item<2-> Let $q$ be the product of the first $p$ numbers.
    \item<3-> Then $q+1$ is not divisible by any of them.
    \item<1-> Thus $q+1$ is also prime and greater than $p$.\qedhere
    \end{enumerate}
  \end{proof}
  \mynote<1>{note one\\}
  \mynote<2>{ note 2\\ }
  \mynote<3>{ note 3\\ }
  \mynote<1>{ note 4\\ }
\end{frame}
\end{document}