It appears to be E-Ink, as it is definitely under the screen, and is a small dot, with lines coming off it, looking a bit like a squashed spider.
Having tried a screen refresh and a hard reset, I took a look at the Amazon site for help. It suggested that for any screen problem, you entered your phone number, and clicked a button – almost immediately my phone rang. By the accent of the guy on the phone, it sounded like he was calling from the States.
I explained the problem to him, who very quickly said “well if you have tried a reset, and it didn’t clear, then it’s a probably not fixable. Your Kindle is under warranty, so I will send you a replacement. Please return your old one in the box the replacement comes in. Enjoy your new Kindle!”
I’ve never found it so easy to return something under warranty!