动画视图关闭屏幕时更改屏幕视图颜色？

I have a listview adapter, and when you click on an item in the list, it opens it up to a full screen activity. I have added a 'swipe to dismiss' functionality within the app. When the user swipes from the left side of the screen, and starts dragging, I set the X position of the top layout in the full screen activity to be the X position of the user's finger. I want to know how to change the color of the gap between the edge of the activity and the edge of the device. It is just white now, but I want it to be transparent to be able to see the adapter below the activity. I have tried setting the background color of the top layout in the full screen activity to be transparent. Here is a crude image describing what I want to achieve. I have a listview adapter, and when you click o