MySQL processes and connections
The blue line shows recently opened connections (i.e. opened since the last sample), while the orange one shows currently opened connections (at the time of sampling). The latter are processes in MySQL (the ones that show when you issue a SHOW PROCESSLIST command to MySQL -- it really means active connections)
This means that most connections stay opened for less than your sampling period. This is a good thing.
I am unable to find official documention for this feature.