[XeTeX] problem with outertheme and color of frametitle

[Stefan Pohl]

Hi list-members,

I have a problem with xetex and the beamer package. If I specify the sidebar
left like this

\useoutertheme[left,width=1cm]{sidebar}
\setbeamercolor{sidebar left}{bg=grey}

I cannot any longer specify the color of the frametitle

\setbeamercolor{frametitle}{fg=blue, bg=orange}

What can I do to solve this conflict? 

Thank you. Stefan.