Only primary Y-axis shall be colored...

Dear Community,

I like to have a simple combined chart:

1. "SALES by PRODUCT CATEGORY" as stacked column on the primary Y-axis
2. "MARGIN" as line chart on the secondary Y-axis

So, it should look like this...

 ...but the PRODUCT CATEGORY (Color drop zone) should only have an effect on SALES, not on MARGIN. So, I want to have ONE line chart for the overall margin. 

(How) Is this possible?

THNAK YOU!!!
Micha