Use case

Current Flutter Material AppBar does not animate the color change from unfilled to filled when user scrolls the page. This sudden change in color is not visually pleasing and looks like a visual glitch rather than intended feature. You can see the current behavior in this demo.

It is possibly not according to Material Design Guidelines as well - see scrolling behavior examples.

Given the amount of effort put into making all sorts of visual transitions smoothly animated, I believe the AppBar behavior should be improved.

Proposal

The change from unfilled to filled AppBar background should be animated as shown in the Material Design Guidelines.