I am using the following code for a beamer presentation:

```
\documentclass{beamer}
\usepackage[brazil]{babel}
\usepackage[utf8]{inputenc}
\usepackage{fancybox}
\title[short version]{SOME TITLE}
%\subtitle[short version]{}
%\date{}
\author[SOME AUTHOR]{SOME AUTHOR}
\institute[SOME INSTITUTE]{SOME INSTITUE}
\usetheme{Pittsburgh}
\begin{document}
\frame{\titlepage}
\begin{frame}[t]

\end{frame}
\end{document}

```

I would like to get a black background colour and white text. How do I get that effect?

Thanks