The protocol for the pa'u skirt is very dependent on the particular situation. There are pa'u skirts ...and then there are Pa'u skirts. In my halau we have our practice pa'u skirt to which I assign very little protocol. We have "costume" pa'u skirts which must be changed quickly at a performance, so there is no time for protocol. And we have our pa'u skirt that is set aside for cultural practice.
Within this last category there are two classes. The first is our white halau pa'upa'u - the term my teacher assigned the pa'u skirt worn together with the tube top used as a garment for the hula. These are the hula garments that we wear when we do a cultural performance with the extended halau when I use one or more classes for a hula presentation.
The second is what I call our sacred pa'u. It is the pa'u given to the student upon the successful completion of her studies as 'olapa. This very special skirt is given to the dancer at her public 'uniki presentation after her sucessful completion of her ritual 'uniki rites. This skirt serves as a confirmation of her having achieved the rank of 'olapa or expert dancer. It is the only "diploma" that the titled dancer receives. This pa'u has been decorated in the traditional way with hand squeezed kukui oil, ash and charcoal to paint on the design. The pattern on the skirt is unique to our lineage. It is the same pattern I wore at my 'uniki as 'olapa, and the same pattern my kumu wore and her kumu before her and on and on. This special skirt is placed on the body with the traditional dressing chants for the kupe'e (wrist and ankle adornments), the lei 'a 'i (neck lei), lei po'o (head lei) and oli pa'u (chant for the hula skirt) for the skirt.
That being said, let us look at what is considered proper protocol when such protocol is appropriate:
Traditionally only dancers having received their rites as 'olapa have a skirt with a design printed on it. Regular dancers had un-decorated pa'u. I am talking very traditional practices, now. Today we buy printed fabric with lovely patterns for our pa'u skirt, but in former days the designs were not only tedious works of art but the design carried the genealogy of the Kumu's hula lineage. Such skirts were, and still are reserved for those dancers who have earned a title.
So you can see that traditions change with time and circumstance. We hold fast to tradition in those most deeply cultural training and rituals that accompany a classic hula training program. But we also move with the times for the ease of daily modern life.