Conditionalized number formats
You can apply different formats when different conditions are met. 
    The condition consists of a comparison operator and a value. Enclose the
      condition in square brackets. For example, [Red]0[<=0];[Blue]£0.00[>0] displays numbers less than or equal to zero in
      red, with no decimal places. It displays numbers greater than zero in blue and as pounds
      sterling to two decimal places. 
To display a graphic when a condition is met, use this syntax:
       [<0][graphic standard_therm_red];[>0][graphic
        standard_therm_yellow];[=0][graphic standard_therm_green]