Green - 1 on top of 2 on top of 3; Blue - 1 on top of 3, but 2 below 3; Red - 1 below 2 below 3; Orange - 1 below 3, 2 above 3.
Nutshell: allows a quick and always apparent check for strategies like the old 8e, 13e, 21e strategy you see online, customizeable by any emas of your choosing.