Цвет текста в узле в стиле Beamer

Question

Я написал простой файл .sty, основанный на теме «metropolis» beamer + fontspec + шрифты Fira. Мне нравится идея на титульном листе, чтобы авторы и учреждения появлялись как в MWE, т. е. одна строка на автора(ов)/учреждение. Недостаток этой компоновки в том, что если я хочу использовать макросы \author и \institution, мне нужно передать аргументы с разделяющей \\формой соавторов, тот же инст. align=leftзаботится об этом. Проблема в том, что новый абзац использует цвет по умолчанию, который является черным, и не более того \usebeamercolor[fg]{author}. Использование color = \usebeamercolor[fg]{author}в определении узла приводит к Missing \endcsname insertedошибке.color = white работает, что я и делаю сейчас, но это означает жесткое кодирование цвета, чего лучше избегать. Решением может быть разделение списка авторов, как вРазделить список \@authors на \ии цикл по авторам, но это выглядит как излишество для того, что я делаю. Есть ли более простой способ применить \usebeamercolor[fg]{author}ко всем авторам?

МВЭ:

\documentclass[11pt, aspectratio=169]{beamer}  % 
\usetheme[]{metropolis}

% Requirement
\usepackage{tikz}
\usepackage{fontspec}

% colors
\definecolor{BGlightBlu}{HTML}{3461AA}

% Fonts
\newfontfamily{\RuLight}{Rubik Light}

% Settings
\setbeamercolor*{author}{fg = white}


% innertheme 

\defbeamertemplate*{title page}{thisStyle}[1][]
{%

\begin{tikzpicture}[remember picture,overlay]
  \draw[fill=BGlightBlu, BGlightBlu] (current page.south west) rectangle
   (current page.north east);

% Title
\node
[   align=left,
    xshift=.6cm,
    yshift = 1cm, 
    minimum width=0.8\textwidth,
    text width=0.7\textwidth,
    anchor = west, 
    font = {\RuLight \LARGE},
    text = white,
    execute at begin node=\setlength{\baselineskip}{0.7\baselineskip}
] (title) at (current page.west)
{
    \inserttitle
};

% Author 
\node
[   
    below=0.6cm,
    align=left,
    anchor = north west,
    xshift=.6cm,
    font={\RuLight \footnotesize},
    align=left,
%   color=white, %works
%     color = \usebeamercolor[fg]{author}, % 'Missing \endcsname' error
    execute at begin node=\setlength{\baselineskip}{01.2\baselineskip}
] (author) at (title.south west){  \usebeamercolor[fg]{author} \insertauthor
                        };  

% Inst
\node
[   
    xshift = 0.5\textwidth,
    below=0.6cm,
    align=left,
    anchor = north west,
    font={\RuLight \footnotesize},
    align=left,
    color=white,
    execute at begin node=\setlength{\baselineskip}{1.2\baselineskip}
] (inst) at (title.south west){ \insertinstitute };

\end{tikzpicture}
}

\title[]{The title is so long that it needs two lines}
\author[]{Me Myself  \\    My First Coauthor, My Second Coauthor}
\institute[]{My Place alone (MPA)  \\ Their place, together (TPT)} 


\begin{document}

\begin{frame}[plain]
\maketitle
\end{frame}

\end{document}

Теперь я разделил код на BgMWE.tex и beamerthemeMWE.sty, чтобы воспроизвести ошибку.

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%  beamerthemeMWE.sty
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\mode<presentation>
\usetheme[]{metropolis}

% Requirement
\usepackage{tikz}

% Settings
\setbeamercolor*{author}{fg = red}

% innertheme 

\setbeamertemplate{background}{
  \begin{tikzpicture}
  \draw[fill=BGlightBlu, BGlightBlu] (current page.south west) rectangle
   (current page.north east);
  \ifnum\thepage>1\relax%
   \fill[white,opacity=1] (0,0) rectangle(\the\paperwidth,\the\paperheight);
   \fi
  \end{tikzpicture}
}

\defbeamertemplate*{title page}{MWE}[1][]
{%

\begin{tikzpicture}[remember picture,overlay]

% Title
\node
[   align=left,
    xshift=.6cm,
    yshift = 1cm, 
    minimum width=0.8\textwidth,
    text width=0.7\textwidth,
    anchor = west, 
    font = { \LARGE},
    text = white,
    execute at begin node=\setlength{\baselineskip}{0.7\baselineskip}
] (title) at (current page.west)
{
    \inserttitle
};

% Author 
\node
[   
    below=0.6cm,
    align=left,
    anchor = north west,
    xshift=.6cm,
    font={ \footnotesize},
    align=left,
    color = author.fg, % Here is the source of the error
    execute at begin node=\setlength{\baselineskip}{0.8\baselineskip}
] (author) at (title.south west){  \insertauthor
                        };  

% Inst
\node
[   
    xshift = 0.5\textwidth,
    below=0.6cm,
    align=left,
    anchor = north west,
    font={ \footnotesize},
    align=left,
    color=white,
    execute at begin node=\setlength{\baselineskip}{0.8\baselineskip}
] (inst) at (title.south west){ \insertinstitute };

\node[below=0.5cm,
     align=left,
     anchor = north west,
     font={ \large},
     color=white,
] (date) at (author.south west){ \insertdate};
\end{tikzpicture}[action]{%
{\usebeamercolor[fg]{author}}% just to initialize the colour
}
}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%  BgMWE.tex
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\documentclass[11pt, aspectratio=169]{beamer}  % 
\usetheme{MWE}


\title[]{The title is so long that it needs two lines}
\author[]{Me Myself  \\    My First Coauthor, My Second Coauthor}
\institute[]{My Place alone (MPA)  \\ Their place, together (TPT)} 


\begin{document}

\begin{frame}[plain]
\maketitle
\end{frame}

\end{document}

Если я скомпилирую MWE.tex, то получуMWE.tex:14: Package xcolor Error: Undefined color `author.fg'.

Type  H <return>  for immediate help.```

Answer 1

Если вы уже использовали цвет автора (простого {\usebeamercolor[fg]{author}}will достаточно), вы можете получить доступ к компоненту переднего плана следующим образом author.fg:

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%  BgMWE.tex
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\documentclass[11pt, aspectratio=169]{beamer}% 


\begin{filecontents*}[overwrite]{beamerthemeMWE.sty}
\mode<presentation>
\usetheme{moloch}% modern fork of the metropolis theme

% Requirement
\usepackage{tikz}

\definecolor{BGlightBlu}{HTML}{3461AA}

% Settings
\setbeamercolor*{author}{fg = red}

% innertheme 

\setbeamertemplate{background}{
  \begin{tikzpicture}
  \draw[fill=BGlightBlu, BGlightBlu] (current page.south west) rectangle
   (current page.north east);
  \ifnum\thepage>1\relax%
   \fill[white,opacity=1] (0,0) rectangle(\the\paperwidth,\the\paperheight);
   \fi
  \end{tikzpicture}
}

\defbeamertemplate*{title page}{MWE}[1][]
{%
\begin{tikzpicture}[remember picture,overlay]

% Title
\node
[   align=left,
    xshift=.6cm,
    yshift = 1cm, 
    minimum width=0.8\textwidth,
    text width=0.7\textwidth,
    anchor = west, 
    font = {\LARGE},
    text = white,
    execute at begin node=\setlength{\baselineskip}{0.7\baselineskip}
] (title) at (current page.west)
{\inserttitle};

% Author 
\node
[   
    below=0.6cm,
    align=left,
    anchor = north west,
    xshift=.6cm,
    font={\footnotesize},
    align=left,
    color = author.fg, % Here is the source of the error
    execute at begin node=\setlength{\baselineskip}{0.8\baselineskip}
] (author) at (title.south west){\insertauthor};

% Inst
\node
[   
    xshift = 0.5\textwidth,
    below=0.6cm,
    align=left,
    anchor = north west,
    font={\footnotesize},
    align=left,
    color=white,
    execute at begin node=\setlength{\baselineskip}{0.8\baselineskip}
] (inst) at (title.south west){\insertinstitute};

\node[below=0.5cm,
     align=left,
     anchor = north west,
     font={\large},
     color=white,
] (date) at (author.south west){\insertdate};
\end{tikzpicture}
}

{\usebeamercolor[fg]{author}}
\end{filecontents*}
\usetheme{MWE}


\title[]{The title is so long that it needs two lines}
\author[]{Me Myself  \\    My First Coauthor, My Second Coauthor}
\institute[]{My Place alone (MPA)  \\ Their place, together (TPT)} 


\begin{document}

\begin{frame}[plain]
\maketitle
\end{frame}

\end{document}