Please have a look
here.
You my need to nest you IIF
Iif(Fields!DBName.Value <> "tempdb",
Iif(Fields!State_desc.Value = "ONLINE", IsNothing(Fields!Physical_device_name.Value),"Orange"
, "LightGreen"),
"LightGreen"),
"LightGreen")
HTH
Thank you but the code is not working