How to change ItemControl item's foreground depending on condition

I have this class:

public class ShippingMethodMap
{
    public string ShippingMethod { get; set; }
    public int? MethodId { get; set; }
    public bool IsManaged { get; set; }
    public bool IsValid { get; set; }
}

Data is stored in ObservableCollection<ShippingMethodMap> ShippingMethodMapCollection, and displayed in XAML like

<ItemsControl ItemsSource="{Binding Path=ShippingMethodMapCollection}">
    <ItemsControl.ItemTemplate>
        <DataTemplate>
            <Border Margin="1" BorderThickness="1" BorderBrush="LightGray">
                <Grid>
                    <Grid.ColumnDefinitions>
                        <ColumnDefinition Width="*"/>
                        <ColumnDefinition Width="50"/>
                    </Grid.ColumnDefinitions>
                    <TextBlock Grid.Column="0"
                               Text="{Binding Path=ShippingMethod}">
                    </TextBlock>
                    <TextBox Grid.Column="1"
                             Text="{Binding Path=MethodId}"
                             IsEnabled="{Binding Path=IsManaged}">
                    </TextBox>
                </Grid>
            </Border>
        </DataTemplate>
    </ItemsControl.ItemTemplate>
</ItemsControl>

Now - how can I set foreground color of TextBlock and TextBox (of distinct Item) to red, if ShippingMethodMap.IsValid = false?

You may add default TextBlock and TextBox Styles with a DataTrigger to the Border's Resources:

<ItemsControl.ItemTemplate>
    <DataTemplate>
        <Border Margin="1" BorderThickness="1" BorderBrush="LightGray">
            <Border.Resources>
                <Style x:Key="BaseStyle">
                    <Style.Triggers>
                        <DataTrigger Binding="{Binding IsValid}" Value="False">
                            <Setter Property="TextElement.Foreground" Value="Red"/>
                        </DataTrigger>
                    </Style.Triggers>
                </Style>
                <Style TargetType="TextBlock"
                       BasedOn="{StaticResource BaseStyle}"/>
                <Style TargetType="TextBox"
                       BasedOn="{StaticResource BaseStyle}"/>
            </Border.Resources>
            <Grid>
                <Grid.ColumnDefinitions>
                    <ColumnDefinition Width="*"/>
                    <ColumnDefinition Width="50"/>
                </Grid.ColumnDefinitions>
                <TextBlock Grid.Column="0"
                           Text="{Binding Path=ShippingMethod}"/>
                <TextBox Grid.Column="1"
                         Text="{Binding Path=MethodId}"
                         IsEnabled="{Binding Path=IsManaged}"/>
            </Grid>
        </Border>
    </DataTemplate>
</ItemsControl.ItemTemplate>