Purple is a beautiful color. But in case it's something in the eyes, maybe see an optometrist, just to be on the safe side. When I close my eyes I see images like I'm having a dream. Some of them are unpleasant so I try to keep my eyes open. But sometimes I'm just too tired & I can't keep them open & I wish those images would stop. Something else in the brain is doing that, maybe for a reason. Another thing I thought of, in relation to your purple dot, is that when I have meditated sometimes I would eventually see the 3rd eye in the center of my inner sight. It's common & real as can be.