Thanks for your reply.
Yes, afterimages are like a prolonged image of what you were just looking at. Mine are the opposite color (dark when looking at a light color; red when looking at a green color), which is considered a normal response, but I seem to have them more often than the average person. For example, I constantly see blue-green blobs while driving/stopping behind vehicles with their brake lights on. It is my number 1 enemy right now!

You say you get these as well? Any other visual phenomenon?
I've been to doctors - opthamologists, optometrists, neurologists, my GP, but no one is too concerned. I do admit to having a bit of health anxiety. These symptoms came on after intense stress about my neurological health (all turned out okay, but then I started having visual problems). My husband is convinced I am just hypersensitive and I agree, but then I see a spot and I start to freak again. I'm pregnant now, so its not like I can go for an MRI or a CAT scan or anything (I have had an MRI for my neurological workup and all is well).
Anyway, I am just trying to cope and convince myself that I am probably okay, but the anxiety is getting to me. I went off Zoloft when I found out I was pregnant, so that may be related, too, I don't know. Thanks for your response!