Do you actually have this, or are these photos off the Internet? I collected and followed this line pretty closely back in the day, including all the variant talk on thegd.com, and I think this is the first time I'm seeing this.
There were two photo variants for the green box 12" Arwen, but neither is the white dress photo pictured here - which is identical to the red box photo. The figure shipped in the green box was always the purple "departure from Lothlorien" version. This white dress figure, to my knowledge, only came out on the red Two Towers packaging and was a pretty rare find even then.
My guess is this is either an overseas release or an early prototype. I say it might be a prototype because if I remember correctly, the earliest photos of the 12" Arwen to be released with Fellowship of the Ring did show her in a white dress - though not the white dress that was eventually released in the red box. (the released version is the white dress she's wearing in her scenes with Aragorn in Lothlorien, the prototype picture had her in the white dress as she appeared to Frodo in the ring-induced-vision in the Trollshaws - all 3 seconds of it)
If you can pick this up for a decent price, its probably well worth it.
