If you have icons of agents State from Health Service Watcher greyed out in the view Monitoring-Operations Manager - Agent Details - Agent Health state you probably need to reset cache of Health service on the server - read this article first:
System Center Data Access Service
System Center Management Configuration
Microsoft Monitoring agent
in out environnement also Veeam services
then delete everythig in C:\Program Files\Microsoft System Center 2012 R2\Operations Manager\Server\Health Service State
restart services - check that folder gets re-populated. Wait a bit and then check SCOM console again if icons became colourful.