Это сложнее, чем я думал. Я сам проверил, и так должно работать:
=IIF(Fields!sg1.Value = "W","Khaki",
IIF(Fields!sg1.Value="g","Gray",
IIF(Fields!sg1.Value="b","Blue",
IIF((LEN(Fields!sg1.Value)=12 And
DateSerial(Mid(Fields!sg1.Value, 7, 2),
Mid(Fields!sg1.Value, 4, 2),
Left(Fields!sg1.Value, 2))
<Today),"Pink", "Green"))))
Откуда 25/10/18
равно Mid(Fields!sg1.Value, 7, 2) = 18 (YY)
, Mid(Fields!sg1.Value, 4, 2) = 10 (MM)
и Left(Fields!sg1.Value, 2) = 18 (DD)
.