%  -*- coding: utf-8 -*-
\documentclass{article}
\usepackage[a4paper,margin=1.5cm]{geometry}

\newcommand*{\myversion}{2022D}
\newcommand*{\mydate}{Version \myversion\ (\the\year-\mylpad\month-\mylpad\day)}
\newcommand*{\mylpad}[1]{\ifnum#1<10 0\the#1\else\the#1\fi}

\usepackage{ninecolors}
\usepackage{arev}
\usepackage{pgffor}
\usepackage{l3draw}
\usepackage{hyperref}
\hypersetup{
  colorlinks=true,
  urlcolor=blue3,
}

\setlength{\parindent}{0pt}
%\setlength{\parskip}{4pt plus 1pt minus 1pt}

\newcommand\NineTestBack{%
\foreach \l in {1,...,9}
{
  \noindent
  \foreach \n in {gray,red,brown,yellow,olive,green,teal,cyan,azure,blue,violet,magenta,purple}
  {%
    \xdef\mycolor{\ifnum \l < 5 white\else black\fi}%
    \colorbox{\n\l}{\color{\mycolor}\strut\n\l}%
  }
  \par
}}

\newcommand\NineTestFore{%
\foreach \l in {1,...,9}
{
  \noindent
  \foreach \n in {gray,red,brown,yellow,olive,green,teal,cyan,azure,blue,violet,magenta,purple}
  {%
    \xdef\mycolor{\ifnum \l < 5 gray9\else black\fi}%
    \colorbox{\mycolor}{\color{\n\l}\strut\n\l}%
  }
  \par
}}

\newcommand\NineTestContrast{%
\colorbox{blue9}{%
  \strut\color{green3}The quick brown fox jumps over the lazy dog. The quick brown fox jumps over the lazy dog.
}
\par\nointerlineskip
\colorbox{green3}{%
  \strut\color{blue9}The quick brown fox jumps over the lazy dog. The quick brown fox jumps over the lazy dog.
}
\par\nointerlineskip
\colorbox{violet9}{%
  \strut\color{brown3}The quick brown fox jumps over the lazy dog. The quick brown fox jumps over the lazy dog.
}
\par\nointerlineskip
\colorbox{brown3}{%
  \strut\color{violet9}The quick brown fox jumps over the lazy dog. The quick brown fox jumps over the lazy dog.
}}

\newcommand\NineTestSaturation[1]{{%
  \NineColors{saturation=#1}
  \noindent\centering
  \colorbox{white}{\makebox[4em]{\strut #1}}%
  \foreach \n in {red,brown,yellow,olive,green,teal,cyan,azure,blue,violet,magenta,purple}
  {%
    \colorbox{\n5}{\makebox[3em]{\strut\rule[-2ex]{0pt}{5.5ex}TEST}}%
  }
  \par
}}

\newcommand\NineTestAllSaturations{%
  \NineTestSaturation{high}%
  \NineTestSaturation{medium}%
  \NineTestSaturation{low}%
}

\ExplSyntaxOn

\cs_generate_variant:Nn \color_fill:n { x }
\cs_generate_variant:Nn \color_stroke:n { x }

\newcommand\NineTestDraw{
  \foreach \l [evaluate=\l~as~\m~using~int(10-\l)] in {1,...,9}
  {
    \noindent
    \foreach \n in {gray,red,brown,yellow,olive,green,teal,
                    cyan,azure,blue,violet,magenta,purple}
    {
      \draw_begin:
        \draw_scope_begin:
          \color_stroke:x { \n\m }
          \color_fill:x { \n\l }
          \draw_path_circle:nn { 0, 0 } { 10pt }
          \draw_path_use_clear:n { stroke, fill }
        \draw_scope_end:
      \draw_end:
      \qquad
    }
    \par
    \vspace*{0.5ex}
  }
}

\ExplSyntaxOff

\begin{document}

\title{\textcolor{blue3}{Ninecolors: Select Colors with Proper WCAG Color Contrast}%
       \footnote{\url{https://github.com/lvjr/ninecolors}}}
\author{Jianrui Lyu (tolvjr@163.com) \\ Nan Geng (nangeng@nwafu.edu.cn)}
\date{\mydate}
\maketitle

\section{LaTeX2 Colors with Medium Saturation}

\textcolor{red4}{Ninecolors} package carefully selects and defines 9 colors for 13 hues each.
All colors with the same suffix number have equal luminance level.
Also color black is of level 0, and color white is of level 10.

\bigskip

\NineTestBack

\medskip

\NineTestFore

\bigskip

By simply choosing two colors in the above list, which differ in level by at least 5,
as foreground and background colors, you will get proper
\href{https://www.w3.org/WAI/WCAG21/Understanding/contrast-minimum.html}{WCAG Color Contrast}.

\bigskip

\NineTestContrast

\bigskip

If you need to select more contrasting foreground and background colors, which may have other hues,
you could visit \href{https://lvjr.bitbucket.io/contrast.html}{WCAG Color Contrast Tool}
page which is designed by the first author.

\newpage

\section{LaTeX2 Colors with Low Saturation}

You can change the saturation of colors by {\color{red3}\verb!\NineColors!} command.
By default {\color{red3}\verb!saturation=medium!}.

\bigskip

\NineTestAllSaturations

\bigskip

\NineColors{saturation=low}
Colors in the remaining part of the page have been changed by
{\color{red3}\verb!\NineColors{saturation=low}!}.

\bigskip

\textcolor{red4}{Ninecolors} package carefully selects and defines 9 colors for 13 hues each.
All colors with the same suffix number have equal luminance level.
Also color black is of level 0, and color white is of level 10.

\bigskip

\NineTestBack

\medskip

\NineTestFore

\bigskip

By simply choosing two colors in the above list, which differ in level by at least 5,
as foreground and background colors, you will get proper
\href{https://www.w3.org/WAI/WCAG21/Understanding/contrast-minimum.html}{WCAG Color Contrast}.

\bigskip

\NineTestContrast

\bigskip

If you need to select more contrasting foreground and background colors, which may have other hues,
you could visit \href{https://lvjr.bitbucket.io/contrast.html}{WCAG Color Contrast Tool}
page which is designed by the first author.

\newpage

\section{LaTeX2 Colors with High Saturation}

You can change the saturation of colors by {\color{red3}\verb!\NineColors!} command.
By default {\color{red3}\verb!saturation=medium!}.

\bigskip

\NineTestAllSaturations

\bigskip

\NineColors{saturation=high}
Colors in the remaining part of the page have been changed by
{\color{red3}\verb!\NineColors{saturation=high}!}.

\bigskip

\textcolor{red4}{Ninecolors} package carefully selects and defines 9 colors for 13 hues each.
All colors with the same suffix number have equal luminance level.
Also color black is of level 0, and color white is of level 10.

\bigskip

\NineTestBack

\medskip

\NineTestFore

\bigskip

By simply choosing two colors in the above list, which differ in level by at least 5,
as foreground and background colors, you will get proper
\href{https://www.w3.org/WAI/WCAG21/Understanding/contrast-minimum.html}{WCAG Color Contrast}.

\bigskip

\NineTestContrast

\bigskip

If you need to select more contrasting foreground and background colors, which may have other hues,
you could visit \href{https://lvjr.bitbucket.io/contrast.html}{WCAG Color Contrast Tool}
page which is designed by the first author.

\newpage

\section{LaTeX3 Colors for Fun}

\NineColors{saturation=medium}

If you are using a LaTeX3 release not older than 2021-07-12,
\textcolor{red4}{Ninecolors} package will define LaTeX3 colors of the same names for you.

\bigskip

For example, you can change the color of drawing operations by
{\color{red3}\verb!\color_fill:n {⟨color expression⟩}!} command
for fills,
{\color{red3}\verb!\color_stroke:n {⟨color expression⟩}!} command
for strokes.
%between {\color{red3}\verb!\ExplSyntaxOn!} and
%{\color{red3}\verb!\ExplSyntaxOff!}.

\bigskip

\NineTestDraw

\end{document}