Greyed Out Enemies
This bug seems a little complicated, but here goes: If you aggro an enemy and attack it (not sure if attacking is required) then deaggro it, it will become grey to you. Following that if you clear the rest of the mobs in it's pack when they spawn they will be grey to you as well.
I tested this in Shadowglen with both non-aggressive and aggressive enemies and it affects both.
Source issue: [url]https://github.com/mangoszero/server/issues/166[/url]