I purchased a Pilot Prera (quite some time ago) and used it as an eyedropper with Parker Quink Blue, Black and Green. I decided to flush the pen out and found that nomatter how much I try, there is a dark-shaded ring left on the inside of the pen body. I can't remember if that "stain" was always there or if that happened because of the ink. So, is this a pen's feature? Does your pen also have it? Thanks in advance! PS. I attach a picture that indicates the ring. Hopefully you can see what I'm talking about.