Using Trulia Heat Maps to Find Wholesaling Areas

I've heard of the "gurus" and virtual wholesalers using trulia heat maps and trends to find the best areas to wholesale in. The thing is I'm not sure how to interpret the info. What's the criteria I should look for to determine what a good area is for wholesaling?

I think it's mostly green areas to find rentals, and anywhere else is a flip/rehab/lease option. Do you go by the areas that are fast movers and shakers?

If anyone can point me to where I can find more info on this or explain it better I'd appreciate it.

Thanks