How to Disable the Blur Effect When Collapsing a `SliverAppBar` in a `CustomScrollView`

问题

1. The Context

I'm trying to make a ListView that has some empty space at the top so the user can bring top cards to the bottom of the screen, where she can easily access them with her thumb. As discussed in this other StackOverflow question, I couldn't make this happen with a regular ListView, so I switched to its parent, a CustomScrollView.

However, after adding a top SliverAppBar, when I get close to collapsing it, the space blurs into darker shades of grey, as seen in the image below. How can I disable this effect?

2. The Code

The `SliverAppBar I'm using so far is:

SliverAppBar(
  automaticallyImplyLeading: false, // gets rid of the back arrow
  expandedHeight: 250, // the collapsible space you want to use 
  flexibleSpace: FlexibleSpaceBar(
    background: Container(
      color: Colors.transparent
    ),
  ),
),

I've also tried to modify my flexibleSpace: FlexibleSpaceBar, but it didn't seem to work:

flexibleSpace: FlexibleSpaceBar(
  title: AnimatedOpacity(
    opacity: 0.0,
    duration: Duration(seconds: 1),
  ),
  collapseMode: CollapseMode.none,
  stretchModes: [
    StretchMode.fadeTitle,
  ],
  background: Container(color: Colors.grey[850]),
),

来源：https://stackoverflow.com/questions/58884360/how-to-disable-the-blur-effect-when-collapsing-a-sliverappbar-in-a-customscro