вот простой пример
<DataGrid AutoGenerateColumns="False">
<DataGrid.Columns>
<DataGridTextColumn Header="Column1" Width="*">
<DataGridTextColumn.CellStyle>
<Style TargetType="DataGridCell">
<Setter Property="Background" Value="LightGreen"/>
</Style>
</DataGridTextColumn.CellStyle>
</DataGridTextColumn>
<DataGridTextColumn Header="Column2" Width="*">
<DataGridTextColumn.CellStyle>
<Style TargetType="DataGridCell">
<Setter Property="Background" Value="LightPink"/>
</Style>
</DataGridTextColumn.CellStyle>
</DataGridTextColumn>
<DataGridTextColumn Header="Column3" Width="*">
<DataGridTextColumn.CellStyle>
<Style TargetType="DataGridCell">
<Setter Property="Background" Value="LightGreen"/>
</Style>
</DataGridTextColumn.CellStyle>
</DataGridTextColumn>
</DataGrid.Columns>
</DataGrid>