\input regression-test.tex
\documentclass{article}
\usepackage[reference-date=2026-07-18]{kanban-board}
\newcommand\kbbrand{kanbanTeal}
\begin{document}
\sbox0{\scriptsize $x$}% Load math font sizes outside captured output.
\START
\makeatletter
\newcommand\kbexpectbackground[3]{%
  \def\kbtask@bg{unset}%
  \kanban@processtaskoptions{#1}%
  \ifdefstring{\kbtask@bg}{#2}
    {\TYPE{#3 OK}}
    {\TYPE{#3 FAILED: \kbtask@bg}}}
\begingroup
  % Capture the diagnostic semantically. The console rendering of l3msg
  % varies across TeX Live releases.
  \ExplSyntaxOn
  \cs_set_protected:Npn \msg_warning:nnn #1#2#3
    {\TYPE{KANBAN~WARNING:~#2~'#3'}}
  \ExplSyntaxOff
  \kbexpectbackground{bg=yellow}{yellow}{KANBAN BACKGROUND NAME}
  \kbexpectbackground{background=orange}{orange}{KANBAN BACKGROUND ALIAS}
  \kbexpectbackground{bg={ teal }}{teal}{KANBAN BACKGROUND TRIMMED}
  \kbexpectbackground{bg=-red}{-red}{KANBAN BACKGROUND COMPLEMENT}
  \kbexpectbackground{bg=red!30!blue}{red!30!blue}
    {KANBAN BACKGROUND EXPRESSION}
  \kbexpectbackground{bg=\kbbrand!60}{kanbanTeal!60}
    {KANBAN BACKGROUND MACRO EXPANDED}
  \kbexpectbackground{bg=}{}{KANBAN BACKGROUND BLANK}
  \kbexpectbackground{bg=nosuchcolor}{}{KANBAN BACKGROUND UNKNOWN NAME}
  \kbexpectbackground{bg=red!50!nosuch}{}
    {KANBAN BACKGROUND UNKNOWN NAME IN EXPRESSION}
  \kbexpectbackground{bg=\emph{x}}{}{KANBAN BACKGROUND ROBUST COMMAND}
  \kbexpectbackground{bg=red!!}{}{KANBAN BACKGROUND MALFORMED}
\endgroup
\begin{kanban}[columns={Light}]
  \kanban@resolvecardback{}
  \ifdefstring{\kb@cardback}{white}
    {\TYPE{KANBAN LIGHT DEFAULT SURFACE OK}}
    {\TYPE{KANBAN LIGHT DEFAULT SURFACE FAILED}}
  \kanban@resolvecardback{yellow}
  \ifdefstring{\kb@cardback}{kb@tintbase!15!white}
    {\TYPE{KANBAN LIGHT TINT OK}}
    {\TYPE{KANBAN LIGHT TINT FAILED: \kb@cardback}}
  \@ifundefinedcolor{kb@tintbase}
    {\TYPE{KANBAN TINT BASE COLOR FAILED}}
    {\TYPE{KANBAN TINT BASE COLOR OK}}
  \kanbantask[bg=yellow,prio=high]{Light}{A tinted light card}
  \kanbantask{Light}{A default light card}
\end{kanban}
\begin{kanban}[columns={Dark},mode=dark]
  \kanban@resolvecardback{}
  \ifdefstring{\kb@cardback}{kanbanInk}
    {\TYPE{KANBAN DARK DEFAULT SURFACE OK}}
    {\TYPE{KANBAN DARK DEFAULT SURFACE FAILED}}
  \kanban@resolvecardback{red!30!blue}
  \ifdefstring{\kb@cardback}{kb@tintbase!20!kanbanInk}
    {\TYPE{KANBAN DARK TINT OK}}
    {\TYPE{KANBAN DARK TINT FAILED: \kb@cardback}}
  \kanbantask[bg=red!30!blue,completed]{Dark}{A tinted dark card}
\end{kanban}
\makeatother
\TYPE{KANBAN BACKGROUND TINTS OK}
\END
\end{document}