Hue / saturation effects - mask on the effect ?

Hi,

I did a thing one time and I can't reproduce it. 🙂
I used a "Hue / saturation" effect. With the hand tool, I selected the green color (the background), and I increased the saturation (image 1). After that, I think a mask layer was created on my effect (image 2). The white zone is the background selected with the hand tool.
When I try again on other images, the mask on the layer is no longer created.

So, I surely forgot one step. Do you have any ideas ?

Thanks a lot !