Chart Help in Numbers

Pretty simple question. I have one data set that goes positive, then negative, and then positive again on the x axis. I want each positive instance to be green, and the negative to be red. I've included a screenshot of how it looks now, but cannot figure out how to get both x-positive periods to both be green. Can anyone help?

 

Could you elaborate a bit more? They're the same column, just at certain points they have negative values (which I want to be red) and at other points it has positive values (which I want to be green)