I recently received an N64 transfer pak. When I looked at the label it was orange, so I looked it up and found that it is a Japanese transfer pak. I am planning on buying an N64 and was wondering whether a Japanese transfer pak would work on a PAL system.
It would appear that the Transfer Paks are compatible no matter which region the system is from.
I'm gathering this information from this article (IGN) which states,
"The Japanese Transfer Pak is completely compatible with US Nintendo 64 systems and games that support the unit."