Where can I find beamercolorbox options defined?

Question

I am trying to understand the \begin{beamercolorbox}[wd=\paperwidth,ht=2.5ex,dp=1.125ex]{palette quaternary} line. I would like to know where it is defined the palette quaternary and if there are other options? Where can I learn about sty?

\documentclass[final]{beamer}
\mode<presentation> {
  % \usetheme{Madrid}
  % \usetheme{Berlin}
  % \usetheme{Rochester}
  \usetheme{Copenhagen}
}
\usepackage[english]{babel}
\usepackage[latin1]{inputenc}
\usepackage{amsmath,amsthm, amssymb, latexsym}
\usepackage{booktabs}
\usepackage{xcolor}
\usepackage{tcolorbox}
\usepackage[orientation=landscape,size=a4,scale=1.2,debug]{beamerposter}

% colors
\setbeamercolor{block body}{fg=black,bg=white}

% beamer template
\setbeamertemplate{headline}{%
\leavevmode%
  \hbox{%
   \begin{beamercolorbox}[wd=\paperwidth,ht=2.5ex,dp=1.125ex]{palette quaternary}%
 \end{beamercolorbox}%
 }

Answer 1

The palette quaternary is defined as \setbeamercolor*{palette quaternary}{fg=white,bg=black} in beamercolorthemewhale.sty, this is one of the colour themes called by the Copenhagen theme.

But you can basically use any beamer colour you like.

\documentclass[dvipsnames]{beamer}

\usetheme{Copenhagen}

\setbeamercolor{mycolor}{fg=RoyalBlue,bg=GreenYellow}

\begin{document}

    \begin{frame}
        \begin{beamercolorbox}[wd=\paperwidth,ht=2.5ex,dp=1.125ex]{mycolor}%
            colored text
        \end{beamercolorbox}%
    \end{frame} 

\end{document}