How do I make a stacked bar graph so that there is no color for the stacked
series unless the data points are greater than 0?

I have two series - the bottom series is blue in color(there will always be
data) - the top series is yellow (the ideal value for my data will hopefully
be zero). When the value of the top series is 0, there is still a yellow top
(not raised) on the blue bar. I would like the bar to be completely blue.
The only way that I can get this to happen is deleting the formula out of the
cell (cell refers to another cell in a different worksheet). Help!