\section{Nuances of \Index{transparency}}

The key value \texttt{\Lkeyword{opacity}=$k$} with $k \in \mathbb{R}$ and $0\leq
k\leq 1$, allows you to define the level of \Index{opacity}.

Within \textit{jps code}, we use an equivalent expression
\texttt{$k$ setfillopacity}. The last expression finds its application in the option \Lkeyword{fcol}. For example the instruction,
\verb+fcol=0 (.5 setfillopacity yellow)+,
which defines the face with the index number 0, sets it to yellow with an opacity of 50\%.

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