Changing the color of a plain frame Metropolis

I’m trying to make some slides for an upcoming presentation with customized colors for the Metropolis theme. However, I’m having some trouble with changing the color for a plain frame (plain). My code now looks like this:

{
setbeamercolor{background canvas}{bg=rugred}
plain{Questions?}
}

Which looks like this:

.

Also, rugredis a custom color, made by myself.

Could anyone help me out and tell me how I can fix this issue? The MWE is given by

documentclass[10pt]{beamer}

usetheme[progressbar=frametitle, block=fill]{metropolis}
%usepackage{appendixnumberbeamer}

definecolor{rugred}{rgb}{0.8,0,0}
setbeamercolor{frametitle}{bg=rugred}
setbeamercolor{plain}{bg=rugred}

usepackage{booktabs}
usepackage[scale=2]{ccicons}

usepackage{pgfplots}
usepgfplotslibrary{dateplot}

usepackage{xspace}
newcommand{themename}{textbf{textsc{metropolis}}xspace}

usepackage{caption}
usepackage{subcaption}
usepackage{graphicx}
usepackage{bm}
usepackage{hyperref}


newcommand{R}{mathbb{R}}
newcommand{N}{mathbb{N}}

title{Title}
subtitle{Presentation}
date{today}
author{Author {and}{Supervisor: hspace{7.2mm} Supervisor} {and}{Second assessor: Second assessor}}
institute{University}

begin{document}

maketitle

{
setbeamercolor{background canvas}{bg=rugred}
plain{Questions?}
}

begin{frame}[allowframebreaks]{References}

  bibliography{references}
  bibliographystyle{abbrv}

end{frame}
end{document}````

documentclass[10pt]{beamer}

usetheme[progressbar=frametitle, block=fill]{metropolis}
%usepackage{appendixnumberbeamer}

definecolor{rugred}{rgb}{0.8,0,0}
setbeamercolor{palette primary}{bg=rugred,fg=white}
setbeamercolor{frametitle}{bg=rugred}

usepackage{booktabs}
usepackage[scale=2]{ccicons}

usepackage{pgfplots}
usepgfplotslibrary{dateplot}

usepackage{xspace}
newcommand{themename}{textbf{textsc{metropolis}}xspace}

usepackage{caption}
usepackage{subcaption}
usepackage{graphicx}
usepackage{bm}
usepackage{hyperref}


newcommand{R}{mathbb{R}}
newcommand{N}{mathbb{N}}

title{Title}
subtitle{Presentation}
date{today}
author{Author {and}{Supervisor: hspace{7.2mm} Supervisor} {and}{Second assessor: Second assessor}}
institute{University}

begin{document}

maketitle

plain{Questions?}

begin{frame}[allowframebreaks]{References}

  bibliography{references}
  bibliographystyle{abbrv}

end{frame}
end{document}