I have done conditional formatting in area chart (shown below, dual chart). The criteria is if the value is less than 0 then " Red" else "Green". However what I have observed (circled by Red color) is
If the April month value is "Red" then further months are all "Red" in spite of Positive values (more than "0").
If I used bar, shape etc then its showing correctly.
When you color a splice of an area chart, you color the entire splice. It won't color the first part red then transition from green. If the transition is important, I would use a column / bar.