That practice is highly illegal and reason for getting cut off from service.
Good point about the other color codes, I should have definitely mentioned that. There are three different kinds that you can find still, the white isn't white though, it is gray, and then, in even older houses but usually only in Groningen and Zeeland if they have not been renovated you can still find cotton/rubber insulation which is super dangerous. If you find any of the older systems codes you should basically just rip it all out and rewire.
Good point about the other color codes, I should have definitely mentioned that. There are three different kinds that you can find still, the white isn't white though, it is gray, and then, in even older houses but usually only in Groningen and Zeeland if they have not been renovated you can still find cotton/rubber insulation which is super dangerous. If you find any of the older systems codes you should basically just rip it all out and rewire.