I like to use the colormix wizard in edit expression,i used expression as sum(countingunits)
i like to show the value with color if the sum(countingunits) value is equal to 0.00,how to use the colormix wizard and where to specify the condition if needed,
When you go to expression tab of your chart you can see a small + symbol in ur expression. Just expand the + symbol then there u will find the property of that expression. There you can give something line below:-
IF(SUM(CountingUnit)=0, RGB(255,0,255))
You can use this for both the Text color as well as backgrond color.