You will have to use an event like PrepareViewStyleInfo to dynamically change the text color.
private void gridControl1_PrepareViewStyleInfo(object sender, GridPrepareViewStyleInfoEventArgs e)
{
double d;
if(e.RowIndex > 0 && e.ColIndex == 2
&& double.TryParse(e.Style.Text, System.Globalization.NumberStyles.Any, null, out d)
&& d < 0)
{
e.Style.TextColor = Color.Red;
}
}