Change gray overlay background of BottomSheet

Short answer : you can't.

The color is hardcoded into the _ModalBottomSheetRoute class (as linked by @pskink) and there is no way to change its value.

New Flutter UPDATE allows you to change the barrierColor in showModalBottomSheet()

showModalBottomSheet(
      barrierColor: Colors.yellow.withOpacity(0.5),

You can actually change this but in order to do so you have to create a copy of this widget file in order to customize it. (steps below are for vscode)

However, by doing this, the widget won't be automatically updated by Flutter because it'd no longer be part of the SDK.

Create A Copy of A Widget To Customize

1. Right-click widget and select Go to definition - this will bring you to the widget's original file

2. Copy all of the code and paste it into a new .dart file with the same name - you'll notice there will now be errors due to a lack of dependencies.

3. In the case of BottomSheet you just need to add import 'package:flutter/material.dart';

4. Now import it like so import 'package:projectname/bottom_sheet.dart' as my; - the as my allows it to use the same .dart file name

5. Now when referencing it just add my. prior like so

my.showModalBottomSheet(
        context: (context),
        isScrollControlled: false,...

Customize Background Overlay Color

Now in bottom_sheet.dart just search for barrierColor and change Colors.black54 to whatever color you want!

I hope this will help anyone in the future!

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Related Question

How to change the background color of BottomSheet in Flutter?