To get back to the original questions, because I just tried doing it with a US kindle and the German kindle store: the US store is the only one showing on a US kindle PW even with the latest firmware and it being available in Germany. There are no settings to change the storefront. Transfers of purchases from the web were possile from whatever store it is registered to.
I asume you may get the same results with a Japanse kindle.
They must have used multicolor LED's and finally realized it. ~ S. attempting to explain the colorful blobs on Kindle Paperwhite screens.