Does a monk wearing a samue break a prātimokṣa vow?

Monks and nuns take the vow of not wearing lay clothes. Zen monks sometimes wear a casual "working clothing" called a *samue*. It looks like a regular kimono, without the belt. Since lay people also wear it, I understand that a samue is actually lay clothes. To distinguish the monks from lay people, the monks have to shave and to wear either the *kasaya* or a small version of it (the *rakusu*). Does a monk wearing a samue break a vow, even when he wears a kasaya or rakusu?