Hi
You can use the lookup function to do this, the lookup function will return the matching id value from table 1.
The lookup function is made up of the following :
Lookup(source_expression, destination_expression, result_expression, dataset)
the conditional expression for formatting the colour will be as follows:
=iif(Fields!Employee_ID.Value = (Lookup(Fields!Employee_ID.Value, Fields!Employee_ID.Value, Fields!Employee_ID.Value, "table_1")), "Red", "Transparent")