This article might be misunderstood as an apologia for racism or a misdirection, so I must start it with a statement:
Please do not mistake an explanation for an excuse.
There is a lot of racism towards non-white people in all of Europe. It is strong in the Slavic nations and it is indeed very strong in Poland, which is currently ruled by a racist covert clerical-fascist party (which luckily does not have overwhelming majority support yet I might add). This does no doubt play a significant role in Poland’s willingness to accept Ukrainian refugees readily, whilst it was refusing Syrians staunchly for the last few years. A policy that I find abhorrent and which should never be in place. Czechia is guilty of the same thing and I oppose that too. I criticize my own government for this and I shall continue to do so.
However, that is most definitively not the sole reason and it might not even be the main reason in this particular case. In my opinion, the main reason here is not that Ukrainian refugees are white, but that the aggressor they are fleeing is Russia and the refugees are Slavs.
There is a lot of panslavic sentiment still floating around (I have written about it before). Slavic people do have a shared identity and they do feel some connection with each other. One of the reasons for that apart from some intelligibility of our languages is that most Slavic nations were oppressed minorities pretty much everywhere for several hundred years, many gaining independence from an oppressive regime only very recently.
But wait, you might say, aren’t Russians Slavs? Yes, they are.
And they are probably the single exception to the rule since they were mostly the oppressors, certainly for the last few hundred years. Poles do not like Russians specifically that much. Russia played for example no insignificant role in destabilizing and partitioning the Polish-Lithuanian Commonwealth in a way that eerily resembles current events in Ukraine. And they did not rule their part of Poland exactly kindly afterward either.
Poles and Ukrainians thus share not only a generic common Slavic identity but also a relatively recent common history. They were both compatriots and allies as well as enemies and rivals in that history, but not very recently and those differences pale with one thing they have common very recently indeed – a ruthless oppressor, Russia. Ukrainians did not forget the Holodomor, Poles did not forget the Katyn massacre and both definitively remember the forty-something years of being dictated what to even think from Moscow afterward.
It is all of course much more complicated than I can ever hope to describe in a short blog post even if I knew everything there is to know about it. And motivations on an individual level always vary wildly. It definitively is not as simple as “Poles think brown people bad, white people good”, although a lot of (not only) Poles are no doubt like that.