I have done in a similar way.

1. you need to add a column with the difference of the Amount, remember to make 0 the difference for the very first value instead of null.

2. For the Top Value, use the regular Amount Field

3. The magic is in the bottom value. it must have the following formula.

=iif(Sum(Fields!DifferenceAmount.Value) = 0, Sum(Fields!DifferenceAmount.Value) ,Sum(Fields!SalesAmount.Value) - Sum(Fields!DifferenceAmount.Value))

4. To make it more understandable you can change the colours with the followinf formula.

=IIF(Fields!SalesAmount.Value >= Previous(Fields!SalesAmount.Value), "Green", "Red")

and done :)