How can I make text alternate color every line?

Question

I'm not referring to tables, just normal paragraphs of text. I want, for example, every other line to be drawn in red, or otherwise highlighted.

My use case is preparing exams for students with special needs.

I thought that something could be worked out maybe calling some TikZ code after the line has been drawn, similar to what packages like lineno do. But that is far beyond my LaTeX skills.

Any help is appreciated.

Answer 1

This is something quickly written with this answer as starting point. It works for plain text but not for equations. Thanks to TikZ' modulo function you could also add a longer color list and alternate between n colors. In principle this can be done without TikZ (e.g. with zrefpos). And it does not require any special compiler like lualatex

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{calc}
\usepackage{soul}
\def\lstcolors{"black","red"}
\newcounter{colorindex}
\makeatletter
\DeclareRobustCommand*\myalternate{%
\begin{tikzpicture}[overlay,remember picture]
\path let \p1=($(0,0)-(current page.south)$) in \pgfextra{
\xdef\lasty{\y1}};
\end{tikzpicture}%
\def\SOUL@everytoken{\begin{tikzpicture}[overlay,remember picture]
\path let \p1=($(0,0)-(current page.south)$) in \pgfextra{
\ifdim\y1<\lasty
 \stepcounter{colorindex}
 \xdef\lasty{\y1}
\fi};
\end{tikzpicture}%
\pgfmathsetmacro{\currentcolor}{{\lstcolors}[mod(\number\value{colorindex},2)]}%
\textcolor{\currentcolor}{\the\SOUL@token}}%
\SOUL@}
\makeatother
\begin{document}
\myalternate{hello hello hello hello hello hello hello hello hello hello
hello hello hello hello hello hello hello hello hello hello hello
hello hello hello hello hello hello hello hello hello hello hello
hello hello hello hello hello hello hello hello hello hello hello
hello hello hello hello hello hello hello hello hello hello hello}
\end{document}