Constant current circuit
The \$V_{BE}\$ of the transistor is about 0.6V, as you said. The rot LED has a \$V_F\$ of about 1.8V, so the voltage across the 470R resistor is about 1.2V. We can ignore the base current, since the BC547 typically has an \$h_{FE}\$ of several hundred. So, the collector current (which equals the LED current) is very close to 1.2V/470R = 2.55mA, regardless of the collector voltage (and therefore the LED drop of the gelb and grun  LEDs). 

Note that this only remains true while the transistor is out of saturation, so the collector voltage of the BC547 must be more than about 1.3V, so the LED string connected to the collector cannot drop more than 9V-1.3V = 7.7V.