Thin white outline around display

[John Davis]

Some how I managed to get a thin white outline around my displays (two). I can click on a display edge and then it goes into a mode where if I hover over the white line at the edge of the display, it disappears. Also if I go into mission control it disappears as well (but comes back as soon as I exit mission control. I just updated to El Capitan, but I don't think that was the cause, I think it started when I was checking out the hot corners option in mission control. Does anyone know what this is and how to get rid of it?

Here is an example (from a screen shot spanning two monitors.)

 

[Cory Cooper]

Hello and welcome.

-What model Mac?
-You stated you have multiple displays, correct?
-Have you tried a PRAM and/or SMC reset?

C