Catholicism has influenced Poland on every level; from political to social and cultural identity. Like in any other society there are different types of believers: devoted Catholics, lukewarm Catholics and lapsed Catholics who, while non-practicing regularly, still appreciate cultural fabric of Poland which is based on Roman Catholicism.
Prof. Boguslaw Wolniewicz, a Polish philosopher, often half-jokingly introduced himself "I'm a secular Catholic". He appreciated Roman Catholicism as a cultural foundation of Polish society.
Roman Dmowski, one of the fathers of Polish Independence in 1918, has wrote "Catholicism is the inseparable essence of Polishness. To remove the Catholic religion and its ethics is to destroy the nation itself"
Anybody who comes to Poland expecting to never see a brown or black face or meet a Muslim, will be disappointed
That depends. Big cities, such as Warsaw have a small minority of non-European foreigners (in Warsaw it's mostly Vietnamese). Those cities also attract tourists from around the world so they may be confused with the actual citizens. Same goes with students from India and African countries.
That said, the most common types of foreigner in Poland are Ukrainians of which there is over a million of them.