For me ketamine visuals mainly consist of closed eye visuals.
With eyes open, and sub k-hole, I tend to get either visual enhancement or a kind of visual degradation, dependent on environment and, to a certain degree, mind state. If it's outdoors and sunny everything can seem really crisp and HD. If it's indoors/dark then things can become pixelated and the red static that covers my vision at a night time becomes very pronounced. I tend to find that the visual static can increase if I'm in a negative mindspace.
With eyes closed, having consumed enough ketamine (but not necessarily in a k-hole), I tend to travel through various black and white/grey landscapes. It's a peculiar sensation but I tend to kind of slide in different directions and enter different rooms, sometimes sliding past figures (who are just part of the scenery and don't appear to be alive), or past the forms of buildings, or down streets and through cities, occasionally lined with the likes of trees. Sometimes I'll speed up and sometimes I'll slow down or change direction, but it generally seems to be at a slow pace. It's always very dark and everything lacks detail.
However, if I sniff enough (at least 1g+) over a long period of time (i.e a couple of hours), and work my way up in very small increments without falling into a full k-hole, then these landscapes can become very crisp, detailed and I think possibly colourful, or at least less dark, and I can pretty much think of something and it will form into the landscape around me.
For the record, this only happens for me with one particular isomer of ketamine, which I believe to be racemic. With the other isomer I just k-hole and don't remember it. I've sniffed my way through grams trying to achieve the same closed eye visuals, working my way up in bumps and doing big lines, and it just doesn't work for me. I think this is probably because I can't remember the k-hole and I'm either in or out.
Obviously it's a very different experience if you're on psychedelics/certain other drugs.