Hi Alex, 

You can use our ConditionalFormatting feature, or you can use the CellControlAttached event:

http://help.infragistics.com/NetAdvantage/Silverlight/2010.3/CLR4.0/?page=xamGrid_Conditional_Formatting.html

As for the event. 

I don't have a sample in VB, however, you simply just need to use the Cell from the EventArgs and validate against it:

something like:

if(e.Cell.Column.Key == "YourColKey")
{
            YourDataObj data = (YourDataObj)e.Cell.Row.Data; 
            if(data.YourColKey == 4)
            {
                     e.Cell.Style = yourRedStyle
            }
}

basically all the code above is doing, is validating your on the column you want to check, 
Grabbing the data from the row, and casting it into your object
Then checking to see if the value is equal to 4, if so, then it sets the cell's style to a predefined style

-SteveZ