\newcommand{\Lang}[1]{\operatorname{\text{\textsc{#1}}}}
+% This gets defined by beamerbasecolor.sty, but only at the beginning of
+% the document
+\colorlet{averagebackgroundcolor}{normal text.bg}
+
\newcommand{\tape}[3]{%
\color{structure!30!averagebackgroundcolor}
\pgfmoveto{\pgfxy(-0.5,0)}