I have been able to see this since I was a toddler. I asked everyone I've known for 30 plus years whether they could see them as well, and everyone said no except my twin brother and father (although my father).
Imagine looking into a room (dark or light) and seeing the space between. In other words, when you look at a wall you see the space (air) between yourself and the wall....
AND... it looks like infinitely small dots colored blue, red and white. It almost looks like a T.V. screen with "Snow" on it (when your T.V. is not tuned to a channel). However the snow is so tiny and yet moves. You can never focus on these miniscule dots because they pop in and out... moving and disappearing. It's actually impossible to focus in on one.
I can see them on my hands, in the air, on everything i look at. When its dark, you can see them better (and with - what seems like colors of red, blue and white).
And depending on the material, the dots can be extreme in an area. If I look at an object the dots seems to be more dense than when I am looking into the air.
Again, this is a real occurrence. I can see them at will. Most times I tune out and choose not to see them... but the moment I think of them... I can see them clearly.... zillions of them.
I have even thought of going to see a hypnotist, and try regressive hypnosis to see if I could find out what they were. My father believes they are atoms. I am not sure whether they are atoms or molecules or something else.... but they are definitely not in my imagination, nor are they a problem with my eyes (or any part thereof).
So... if anyone has this ability or knows what the heck I'm talking about, please let me know. If anyone has any questions... please ask and I'll try to answer them. I would really love to find out, after decades, what they are and if anyone else sees them.