Why do I get a sort of strip passing through the frame title when using the dvipsnames option of xcolor in beamer?

Question

Consider the following minimal example:

\documentclass[9pt, xcolor=dvipsnames]{beamer}
\mode<presentation>
{
  \usetheme{Frankfurt} 
  \usecolortheme[named=OliveGreen]{structure}
}
\begin{document}
\begin{frame}

    \frametitle{Test title}

\end{frame}
\end{document}

I get surprisingly a sort of strip passing through the frame title when using, for instance, the OliveGreen color. This issue somehow disappears when using a classical color such as blue or green. Any thoughts how this could be fixed?

Thank you!

Answer 1

You can avoid the problem by explicitly selecting a colour model:

\RequirePackage[cmyk,dvipsnames]{xcolor}
\documentclass[9pt]{beamer}
\mode<presentation>
{
  \usetheme{Frankfurt} 
  \usecolortheme[named=OliveGreen]{structure}
}
\begin{document}
\begin{frame}

    \frametitle{Test title}

\end{frame}
\end{document}