material_color_generator.dart

import 'dart:math';
import 'package:flutter/material.dart';

MaterialColor generateMaterialColor(Color color) {
  return MaterialColor(color.value, {
    50: tintColor(color, 0.5),
    100: tintColor(color, 0.4),
    200: tintColor(color, 0.3),
    300: tintColor(color, 0.2),
    400: tintColor(color, 0.1),
    500: tintColor(color, 0),
    600: tintColor(color, -0.1),
    700: tintColor(color, -0.2),
    800: tintColor(color, -0.3),
    900: tintColor(color, -0.4),
  });
}

int tintValue(int value, double factor) =>
    max(0, min((value + ((255 - value) * factor)).round(), 255));

Color tintColor(Color color, double factor) => Color.fromRGBO(
    tintValue(color.red, factor),
    tintValue(color.green, factor),
    tintValue(color.blue, factor),
    1);

Hello, Moritz.
I'm trying to implement this snippet for custom material color schemes. And unfortunately getting the same issue. Could you kindly advise on how to solve it?

Got it! Sorry, was my bad. It was the primary color, which had to be fully opaque. Thank you for the gist!

Works perfectly.