BackgroundValueConverter.cs

public sealed class BackgroundValueConverter : IValueConverter
    {
        public object Convert(object value, Type targetType, object parameter, string language)
        {
            var passwordStrength = int.Parse(value.ToString());
            
            if (passwordStrength > 33 && passwordStrength <= 66)
            {
                return new SolidColorBrush(Colors.Orange);
            }
            
            if (passwordStrength > 66)
            {
                return new SolidColorBrush(Colors.Green);
            }

            return new SolidColorBrush(Colors.Red);
        }

        public object ConvertBack(object value, Type targetType,
            object parameter, string language)
        {
            throw new NotImplementedException();
        }
    }