In Austria the book says this: Blue is only to be used as a neutral and all neutrals have to be blue. y/g is ground only. Only exception to the rule: grey (as in NYM-J 4x1,5) can be sleeved blue as a neutral. After the changes suppliers ran out of blue heatshrink tube.
Phases can be about any color except blue, y-g, yellow and green (not sure about the two latter, might be just Germany). The Germans just switched back to grey neutrals when using such cable [Linked Image]