All shoots appear pink and during the spring, even leaves remain pink for a while - well, the white parts. I've read that it reverts to all green when summer arrives and is only variegated during the spring. There is another variegated version, called Peppermint stick, that keeps variegation during whole year. I guess it's Arundo donax 'Peppermint stick' then.
The pink color is going to fade out in a week or two, when it gets taller. I think only a couple of protective sheaths will appear pink, after that they are usually pink around edges and then it fades completely. It must be cold related, when it's cold, the pink color will remain as plant grows and even appear on some existing leaves (I noticed that last autumn). Bamboos, especially variegated versions often do the same. Shiroshima for example.