Players are changing this setting to make enemies have a brighter glow.

As I was perusing social media, I began to notice that players had their enemies outlined in a yellow glow. I thought it was spectator mode or a replay, but I realized their enemies were glowing during a live match.

I looked into it and realized everyone was using settings designed to aid those with color vision impairment. So apparently if you turn on colorblind mode, you can see all your enemies in full color plus an extra glow.

You see how wild that image is. This definitely makes it easier to spot enemies. It will also change a couple graphics, but the only one I could notice was the red barrier walls on the mini map changed to yellow.
You can access this setting in the General tab and at the very top, the 2nd option is Enemy Highlight Color. You can choose between purple or yellow, the latter being much easier to see.

You can watch me play with the yellow setting on.