That's called the
$1 and it is indeed exactly what you think it is. Hallucinations that occur after vision loss as the brain adjusts to no longer having any input coming into the vision center. I lost my vision very suddenly back in 2014 from a retinal arterial occlusion, and I had this syndrome for a few months. I'd "see" a fiery red-orange circular field in the center of my vision, or sometimes it would be a bright electric blue. I'd wake up from very vivid dreams that had one of those colors feature very prominently in them and it would take a while for the color field to fade away.
It's harmless and nothing can be done about it, so you just have to ride it out.