What the regulations ask forPaint in the common areas, and fire
Inside the flats the table does not apply. In the common areas it does: the Spanish Building Code (Código Técnico de la Edificación, CTE) sets a minimum reaction-to-fire class for wall, ceiling and floor finishes.
This is table 4.1 of the Building Code’s Documento Básico on fire safety. The first row includes circulation areas that are not protected and expressly excludes the inside of dwellings. And the requirement applies when the finish covers more than 5% of the walls, the ceilings or the floors of the space.
In practice, what you need to do is ask for the product data sheet to state its class. It matters most for things that are not paint: vinyl wallpaper in the entrance hall, timber panelling, a decorative plastic wall covering. That is where an attractive finish may not be up to the standard of the area where it goes.