What variable contains the word “Appendix” when a chapter is an appendix?

Question

I've designed a whole new fancy chapter header layout, and have hard coded the word "Chapter" in there before the chapter number. I just realized now that this won't work because I have an appendix named "Chapter A".

Is there a variable that will contain the word Chapter or Appendix depending on which it is typesetting at the moment? \chaptername only seems to have the word "Chapter" even though I'm using it under the appendix section.

Edit: I've got it working in my chapter headers, thanks to answers below; but my TOC isn't working properly. I've changed my TOC with titletoc, and it still says "Chapter" even though I've got the following code:

\documentclass{book}
\usepackage{titletoc}
\usepackage{color}

\makeatletter
\titlecontents{chapter}[-2em]
    {\color{cyan}\bfseries\LARGE\addvspace{3mm}}
    {\@chapapp \contentslabel{-0.25em}\hspace{2em}}
    {}
    {\hspace{3em}\contentspage}
\makeatother

\begin{document}
    \tableofcontents
    \chapter{test}
    \appendix
    \chapter{asdf}
\end{document}

Answer 1

In the standard classes book and report, the \chapter command uses the internal command \@chapapp to typeset chapter headings. \@chapapp is initially defined as \chaptername ("Chapter"), and redefined to \appendixname ("Appendix") as soon as you issue \appendix in the document body.

In response to your follow-up question: Here's one (possibly not the most elegant) way to achieve correct naming in the ToC:

\documentclass{book}
\usepackage{titletoc}
\usepackage{color}

\makeatletter

\titlecontents{chapter}[-2em]
    {\color{cyan}\bfseries\LARGE\addvspace{3mm}}
    {\@chapapp \contentslabel{-0.25em}\hspace{2em}}
    {}
    {\hspace{3em}\contentspage}

\g@addto@macro{\appendix}{%
  \addtocontents{toc}{\protect\renewcommand*{\protect\@chapapp}{\protect\appendixname}}%
}

\makeatother

\begin{document}
    \tableofcontents
    \chapter{test}
    \appendix
    \chapter{asdf}
\end{document}

Answer 2

If you use titlesec, then the command you look for is \chaptertitlename that defaults to \chaptername, but it is \appendixname in the appendix.