When I superpose two \path [fill=...] that should match exactly, I get an outer lining from the first fill.
It doesn't appear to be a shortcoming of the pdf viewer, as it also shows once converted to png.
How to get around this ?
MWE
\documentclass[tikz,border=10pt]{standalone}
\begin{document}
\begin{tikzpicture}
\path [fill=black] (0,0) rectangle (1,1) ;
\path [fill=white] (0,0) rectangle (1,1) ;
\end{tikzpicture}
\end{document}
