Weelll… that page lists the #ffffff version of the flag of Poland [0]. The law specifies the color using a strange color scale (CIELUV [1]), and it was written in the 1980s with fabric in mind, which cannot be a pure white - so the color translates to #E9E8E7, looking like [2]. This was the subject of a flamewar on Polish Wikipedia around 2006, which also involved a light-pink version [3] due to someone miscalculating the colors. In the end, en.wiki uses the #fff version [4], and pl.wiki uses the grey version in the flag article [5] and the white version anywhere else [6].

And a few months ago, the government proposed an amendment to the law. That lists #ffffff as the official color (for non-textile use). But it will probably take some time until it actually goes into force, if it ever will…

tl;dr: colors are hard, flag colors specified by 1980s laws doubly so.

[0] https://commons.wikimedia.org/wiki/File:Flag_of_Poland.svg [1] https://en.wikipedia.org/wiki/CIELUV [2] https://commons.wikimedia.org/wiki/File:Flag_of_Poland_(norm... [3] https://commons.wikimedia.org/wiki/File:Flaga_Polski_strange... [4] https://en.wikipedia.org/wiki/Flag_of_Poland [5] https://pl.wikipedia.org/wiki/Flaga_Polski [6] https://pl.wikipedia.org/wiki/Polska

... and aspect ratios. Country flags are not (almost) squared as in the OP link.