Overview in supplier, customer, project pages

Good day to all

Looking at the green dots in the overview section on the following pages

The explanation says
This os based on transactions against this “Customer”

I don’t see any link between the dates where there are green dots and the sales order / invoices ?
Or does it refer to actual dates when there were activity i,e, actual dates not posting dates ?

Also, what does the different colors of green refer to ?

I have googled this but I must be using the wrong key-words because sofar, my search has yielded
nothing . Could someone assist please ?