# Latex beamer block shadow fades to white and not to the background color

I modified the background color using \setbeamercolor{background canvas}{bg=blue!25}. However, the shadow of the blocks fade from black to white and not to the background color (resulting in a tiny white stripe around the shadow before the background color takes over), see code below.

I found the following fix How to add a transparent shadow to a block in beamer?

(there the white line around the shadow can also be seen clearly)

However, the modified version of beamerbaseboxes.sty seems to be outdated, since it changes the appearance of the whole presentation, not only the shadows. Since I do not want transparent shadows but merely shadows that fade into the background color, I would like to ask how to achieve this without hacking the beamerbaseboxes.sty file.

\documentclass{beamer}

\setbeamercolor{background canvas}{bg=blue!25}

\begin{document}

\frame{
\begin{block}{test block}
block block
\end{block}

}

\end{document}

-

The following code will give the expected output:

\documentclass{beamer}

\usepackage[T1]{fontenc}
\setbeamercolor{background canvas}{bg=blue!25}

\makeatletter
color(0bp)=(blue!25); color(4bp)=(black!50!bg); color(8bp)=(black!50!bg)}
color(0bp)=(black!50!bg); color(4bp)=(blue!25)}
color(0bp)=(black!50!bg); color(4bp)=(black!50!bg); color(8bp)=(blue!25)}
%
\makeatother

\begin{document}

\frame{\frametitle{l}
\begin{block}{in a block}
default font
\end{block}
}

\end{document}


Please note: this is of course a hack to beamerbasebox since the original definitions are overwritten. I do not know if there could possibly be any side effects. (Those shadows could be used anywhere else...). And of course i have no idea why it does not choose the background color automatically.

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Thank you very much for this solution. Do you think this should be reported as a Bug to the beamer-developers? – 7asd44 Jan 20 '13 at 14:19
Well if you do understand the code completely go on... I wouldn't claim that for me and therefore i could not write a qualified report. I'm still struggling in finding out how the color is actually chosen for the rounded boxes. – bloodworks Jan 20 '13 at 14:29
If you dont feel qualified to write the bug report, I do neither :) Thank you again for the fix! – 7asd44 Jan 20 '13 at 15:11