The blue color indicates that either one or more of the configured devices are not responding to the polls and requests of the OPC Server. This is usually the case when you have multiple devices configured on the OPC Server and while polling, any one of the devices may have gone offline.

Check the GUI of the OPC Server to see if there is anything like “Value Bad” in the value column. If there is a ‘Value Bad’ then that device is offline. This shows that the OPC Server was unable to get a fresh value for that property because that device is offline or not responding completely.