What is the right course of action?

In the scenario presented, the correct actions involve allowing the blue vehicle to pass and turning before the green vehicle. This is based on the right-of-way rules articulated in German traffic regulations.

When layout and traffic signs indicate that you have to yield to an approaching vehicle (in this case, the blue vehicle), you must let that vehicle go first. After that, if conditions permit, you may make your turn before the green vehicle despite being in a conflict.

This combination is essential to ensure safety and proper traffic flow, as it maintains the right order of movement and respects the regulations regarding priority at intersections. Always check for road signs and the behavior of other vehicles to make informed decisions.