SSRS InScope() function: The key to format your matrix!

The InScope() function checks to see if the current item is in the specified scope.
For a basic matrix report with the use of ‘Totals’ on both axes:

The Green cells fall out-of-scope of the ColumnGroup, and In-Scope for the RowGroup
The Grey cells fall out-of-scope of the RowGroup, and In-Scope for the ColumnGroup
The Light blue cells fall In-Scope of both the ColumnGroup and the RowGroup.
The Dark blue cell falls out-of-scope of both the ColumnGroup and the RowGroup.

Expression example code:

=IIf(InScope(“ColumnGroup”),
IIf(InScope(“RowGroup”),”LightBlue”, ”Grey”),
IIf(InScope(“RowGroup”),”DarkGreen”, “DarkBlue”)
)

Thanks to Luke Hayler for his great example.