I did hear the powder pink was limited edition for the spring/summer 2017 collection... I was hoping to find itMaybe it sold out since it was seasonsl and SA only knows about products that are available now... I happened to watch Shea Whitney's review of the bag, a youtuber, and fell in love with the color...
They are definitely two separate colours - Rose Poudre and Powder Pink. I found it odd too, but I confirmed this with my SA when I was deciding which Diorama to get. I was deciding between the old and new Rose Poudre - both are light pink, one in grained calfskin and one in supple grained calfskin. The more mauve colour is called Powder Pink, it is the colour of my Lady Dior and it also came in the Diorama but it sold out. Very confusing, but they are definitely two separate colours.
ETA: I saw both Rose Poudre bags in person when I was deciding which to buy and they were both a light pink, not mauve at all. The tag says Rose Poudre - the tag for my LD said Powder Pink.