[flexcoders] Can't style AdvancedDataGrid GroupingField

[fumeng5]

Hi, 

I set a styleFunction for my AdvancedDataGrid:

private function styleRows(data:Object, column:AdvancedDataGridColumn):Object{
                return {
                                        verticalAlign:'middle',
                                        backgroundColor:"0xeaeaf4",
                                        borderColor:"0xbcdbcd9",
                                                        borderStyle:"solid",
                                                        borderThickness:"1"
                }
                        }

It styles all my columns correctly except the first one (which is my 
GroupingField) doesn't get its backgroundColor or borders set. Why might this 
happen? Here's my AdvancedDataGrid dataProvider and columns set below:

<mx:dataProvider>
            <mx:GroupingCollection id="gc" source="{appColl}">
                <mx:grouping>
                    <mx:Grouping>
                        <mx:GroupingField name="label"/>
                    </mx:Grouping>
                </mx:grouping>
            </mx:GroupingCollection>
        </mx:dataProvider> 
        
        <mx:columns>
            <mx:AdvancedDataGridColumn 
                dataField="label"
                width="175"/>
            <mx:AdvancedDataGridColumn 
                width="300"
                itemRenderer="com.renderer.ApplicationIndicatorRenderer"/>
            <mx:AdvancedDataGridColumn 
                width="300"
                itemRenderer="com.renderer.ApplicationIndicatorRenderer"/>
            <mx:AdvancedDataGridColumn 
                width="300"
                itemRenderer="com.renderer.ApplicationIndicatorRenderer"/>
        </mx:columns>