Is anyone here any good with SSRS Colour Expressions. I well believe I have coded it correctly but it doesn't appear to be working. I'm not sure if this could be a bug within Visual Studio 2017 or what. Can anyone advise?

The value is 0 for the field but yet its still showing the colour as Red, when it should be green?

Code:
=Iif((Sum(Microsoft.VisualBasic.Interaction.IIF(Fields!STATUS_TYPE_ID.Value = 1 AND IsNothing(Fields!FIELD_1.Value), 1, 0), "CallDetails")) <= 2, "SeaGreen", Iif((Sum(Microsoft.VisualBasic.Interaction.IIF(Fields!STATUS_TYPE_ID.Value = 1 AND IsNothing(Fields!FIELD_1.Value), 1, 0), "CallDetails")) > 6, "Red", "DarkOrange"))