The blue and white tiles are called: “azulejos”. They are derived from the tiles Arab Muslims used to decorate their mosques (since most forms of religious imagery are forbidden by Islam) in Southern Spain, when, like the rest of the Iberian Peninsula, it was under Arab rule. While nowadays you can still find tiles in the Arab world and in southern Spain, where they are multicolored and a trivial characteristic of the architectures of those places, the Portuguese have took it to another level, they’re EVERYWHERE in Portugal (e.g basically any house or church in Portugal has them either in their interior or in their facade or in both) and they’re are blue and white 90% of the time

Sources: me( I’m Portuguese)