Hello Oliver,

You can accomplish this by using some client-side code.

First handle the Initialize client-side event fired by the WebDataGrid control.

<ig:WebDataGrid ID="WebDataGrid1" runat="server">

        <ClientEvents Initialize="initialize" />

</ig:WebDataGrid>

The handler will look like this:

function initialize(sender, eventArgs) {

        //gets all rows
        var rows = sender.get_rows();
        //iterates through the rows
        for (var i = 0; i < rows.get_length(); i++) {
            //gets the current row
            var row = rows.get_row(i);
            //gets the first and the second cell of the current row
            var cell1 = row.get_cell(0);
            var cell2 = row.get_cell(1);

            //compares their values
            if (cell1.get_value() > cell2.get_value())
                //adds a class with custom properties for the cell
                cell1.get_element().classList.add('red');
            else
                cell1.get_element().classList.add('green');
        }

}

This example expects two classes to be added to the stylesheet.

.red
{
    background-color: Red ! important;
}
.green
{
    background-color: Green ! important;
}

Hope this helps. Please let me know if you need further assistance.

Best regards,

Stamen Stoychev