Hi,
Don't worry, its a common question.
Observium saves the 5min pollingdata for 48h, then it begins to aggregate by taking the 5min-values and aggregate them together in a 30min average.
This makes any traffic peaks a lot smaller as the peak will be averaged out with the other data and because of that Observium also saves the peak value for every 30min period.
This value is the "light-shade" green higher value and the darker green is the 30min average value.
The green inside the graph (lowest arrow) is just a filling colour to make the graph look better.
/Markus