These are the cartridges you need to refill the Plumix. I got the blue-black
refill cartridges and thought ink came out looking a bit too gray.
You could also flush out the empty cartridge and refill using your choice of
bottled fountain pen inks (which come in a huge variety of colors) with a blunt
tipped syringe (I went to the local pharmacy and asked for a syringe with the
sharp removed). I have heard that you do need to keep the little purple disc in
the cartridge to maintain proper ink flow.
Got these as part of a gift for a friend. Though I have not tried the ink
myself, he told me that he really enjoys using them with his Pilot Metropolitan
and that the ink color and quality are very good, and behaves pretty well with