如何自定义DevExpress.DXGrid for WPF单元格样式？

<Window x:Class="DXGrid_ConditionalFormatting.Window1"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="clr-namespace:DXGrid_ConditionalFormatting"
xmlns:dxg="http://schemas.devexpress.com/winfx/2008/xaml/grid"
xmlns:dxgt="http://schemas.devexpress.com/winfx/2008/xaml/grid/themekeys"
Title="Window1" Height="300" Width="470">
<Grid>
<dxg:GridControl x:Name="grid">
<dxg:GridControl.Resources>
<Style x:Key="customCellStyle"
BasedOn="{StaticResource {dxgt:GridRowThemeKey ResourceKey=CellStyle}}"
TargetType="dxg:CellContentPresenter">
<Setter Property="Background"
Value="{Binding Path=RowData.Row.UnitsOnOrder, Converter={local:IntoToColorConverter}}"/>
</Style>
</dxg:GridControl.Resources>
<dxg:GridControl.Columns>
<dxg:GridColumn FieldName="ProductName"
CellStyle="{StaticResource customCellStyle}">
Product
</dxg:GridColumn>
<dxg:GridColumn FieldName="UnitPrice">
Unit Price
</dxg:GridColumn>
<dxg:GridColumn FieldName="UnitsOnOrder">
Units On Order
</dxg:GridColumn>
</dxg:GridControl.Columns>
<dxg:GridControl.View>
<dxg:TableView AutoWidth="True" />
</dxg:GridControl.View>
</dxg:GridControl>
</Grid>
</Window>