I am no sushi/Japanese food connesieur, however, from my (limited) understanding is that the pink ginger is typically the bulk stuff you get out of Thailand and is not fresh.
The yellow ginger (again, due to my limited understanding) is generally made fresh and in-house. That being said, if a place is going to serve the yellow ginger, it generally suggests that a level of quality is maintained in regards to the food they serve.
Somebody who is more knowledgable on the topic of Japanese/Sushi will correct me.
