SSRS Reporting : Fill Cell Color according to the Location of the Cell in the Matrix

Hello,

I am trying to achieve below result in the SSRS but facing issues with Cell color Fill Expression when Detail value is NULL.

If you look at the image, it should show exact same colors of the cell irrespective of the values.

But in my case it is not showing color for NULL value cells.

Below is the expression which I have put in the Fill Expression window.

SWITCH(
Fields!Columns.Value = "Col1" And Fields!Rows.Value = "Row1","Yellow",
Fields!Columns.Value = "Col1" And Fields!Rows.Value = "Row2","Green",
Fields!Columns.Value = "Col1" And Fields!Rows.Value = "Row3","Green",
Fields!Columns.Value = "Col1" And Fields!Rows.Value = "Row4","Green",
Fields!Columns.Value = "Col2" And Fields!Rows.Value = "Row1","Red",
Fields!Columns.Value = "Col2" And Fields!Rows.Value = "Row2","Yellow",
Fields!Columns.Value = "Col2" And Fields!Rows.Value = "Row3","Yellow",
Fields!Columns.Value = "Col2" And Fields!Rows.Value = "Row4","Green",

Fields!Columns.Value = "Col3" And Fields!Rows.Value = "Row1","Red",
Fields!Columns.Value = "Col3" And Fields!Rows.Value = "Row2","Red",
Fields!Columns.Value = "Col3" And Fields!Rows.Value = "Row3","Yellow",
Fields!Columns.Value = "Col3" And Fields!Rows.Value = "Row4","Green"
)

Please suggest me to get the colors for the NULL value cells.

I tried with IsNothing() but then it is doing the same color of all NULL cells. I want them exactly same in the figure.

Thank you,

Mittal.