<DataGrid AutoGenerateColumns="False">
    <DataGrid.Columns>
        <DataGridTextColumn Width="*" Binding="{Binding Date}" Header="Date"/>
        <DataGridTextColumn Width="*" Binding="{Binding Category}" Header="Category"/>
        <DataGridTextColumn Width="*" Binding="{Binding Amount}" Header="Amount"/>
        </DataGridTextColumn>
    </DataGrid.Columns>
</DataGrid>

public class TransactionDto
{
    public long Id { get; set; }
    public decimal Amount { get; set; }
    public string Category { get; set; }
    public DateTime Date { get; set; }
}

public class AmountConverter : IValueConverter
{
    private const decimal Threshold = 0.00m;
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        return (decimal)value >= Threshold;
    }
    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        throw new NotImplementedException();
    }
}

<Page.Resources>
<Style TargetType="DataGridRow">
    <Style.Triggers >
        <DataTrigger Binding="{Binding Amount, RelativeSource={RelativeSource Self}, Converter={StaticResource ResourceKey=AmountConverter}}" Value="False">
            <Setter Property="Foreground" Value="Red"/>
        </DataTrigger>
        <DataTrigger Binding="{Binding Amount}" Value="-24.71">
            <Setter Property="Foreground" Value="Green"/>
        </DataTrigger>
    </Style.Triggers>
</Style>