The white used on earlier V7 Classics (white diamond) was code 00BM (usually abbreviated to just BM). The code for the 2016 Stornello's tank appears to be 00XB, but that's not for sure. Figuring these things out takes careful review of the parts manuals, particularly where there was only one color for that machine - then the paint code often doesn't even appear for the part (unless the same part is used on other models).
Piaggio uses the same codes across all product lines (in most cases), so you can search for Vespa, Piaggio, Aprilia, etc. and that code and see what you find. They may have sold a model in another line with the same paint.