*Two* colored swatches

Question

Baically, do Coloured swatch per chapter but do two of them, each half an inch tall and stacked.

Something like \swatches{black}{yellow}?

Answer 1

Suggestion:

\documentclass
  %[oneside]
{book}
\usepackage{xcolor}
\usepackage{blindtext}

\usepackage[
  automark,
  autooneside=false,
  markcase=noupper,
  headsepline,
  headwidth=\the\textwidth+12mm:-5mm,
]{scrlayer-scrpage}
\clearpairofpagestyles
\rehead{\leftmark}
\lohead{\rightmark}
\ohead{\pagemark}
\renewcommand\chaptermarkformat{}% no chapternumber in header
\setkomafont{pageheadfoot}{\normalfont}

% define new layers
\DeclareNewLayer[
  background,
  oddpage,
  align=tr,
  hoffset=\paperwidth,
  voffset=0pt,%distance from top
  width=1cm,% width of the swatch
  height=1in,% height of the swatch
  mode=picture,
  contents={%
    \put(0,\LenToUnit{.5\layerheight}){\textcolor{swatchcolor1}{\rule{\layerwidth}{.5\layerheight}}}%
    \putLL{\textcolor{swatchcolor2}{\rule{\layerwidth}{.5\layerheight}}}%
  }
  ]{swatch.odd}
\DeclareNewLayer[
  clone=swatch.odd,
  evenpage,
  align=l,
  hoffset=0pt
  ]{swatch.even}

% add layers to every pagestyle
\AddLayersToPageStyle{@everystyle@}{swatch.odd,swatch.even}

\newcommand\swatchcolors[2]{\colorlet{swatchcolor1}{#1}\colorlet{swatchcolor2}{#2}}
\swatchcolors{white}{white}

\begin{document}
\tableofcontents
\chapter{First chapter}\swatchcolors{black}{yellow}
\section{First section}
\Blindtext[20]
\chapter{Second chapter}\swatchcolors{gray}{orange}
\section{First section}
\Blindtext[20]
\chapter{Third chapter}\swatchcolors{blue!80!black}{purple}
\section{First section}
\Blindtext[20]
\end{document}