(just skimming) I am guessing the y-axis is the observed expected value of the treatment (low being good) and the dots are re-colered to null if the sample size

(just skimming) I am guessing the y-axis is the observed expected value of the treatment (low being good) and the dots are re-colered to null if the sample size was too small to separate the (not shown) error bars around the dot from no effect. The punchline is: once the researchers had to declare their statistical procedure before turning in the results most of the dots get colored "null." Meaning the strongest effect in the past was the ability to argue your way into a more favorable analysis.