Slicing cumulative data by a third field

I am trying to create a stacked bar chart that represents cumulative data and shows a third category for the growth.  I used the DAX formula suggested by others to successfully create cumulative data (thank you!!), but I'm not able to show separate colors for contributions to growth.  

For example, say I have 5 sales people, and I want to show cumulative sales by month over one year.  In February I want one color (say green) to be January's sales, and then to show who contributed to February's sales I want to show Jen's sales in black, Bob's in blue, Kim's in yellow, etc.  

So far I've been able to create cumulative data, or the individualized color data, but I haven't been able to combine these two approaches.  Can anyone help?