I have noticed with operations manager 2016 that by default the agent enters a grey state on all domain controllers. This looks to be caused by a permissions problem with either the local system account (Or your alternative if you have configured one) Fortunately it is a simple fix. Assuming you have winrm setup and working and have administrator access the following should resolve the issue for you:
1. Connect to the server with the grey status:
WINRS -r:MYDCNAME01 cmd.exe
2. Change directory to the Agent location:
cd “C:\Program Files\Microsoft Monitoring Agent\Agent”
3. use the hslockdown program to permit your useraccount.
HSLockdown.exe /A “NT AUTHORITY\SYSTEM”
and/or
HSLockdown.exe /A “mydomain\someaccount”
4. Stop and start the health service:
net stop healthservice
net start healthservice
Your agent status should shortly turn green. Happy monitoring!