The blue line shows the motion of the rotor blade, moving forward due to rotation. The green line shows the relative wind. Since there is only a horizontal component to motion right now, the green line is horizontal. The pink line labeled tip plane path shows the orientation of the rotor disk. It's just another line showing the horizontal motion of the rotor blade.
Angle of attack is defined as the angle between the relative wind and the chord line.
That is shown by the purple line. The way I've drawn this is on top to show the two components of motion of the rotor blade. Note that the blade is flapping up . I've copied the blue lines of motion down by the airfoil, and used the red lines to show where we would extend the blue lines to. Then I drew the green relative wind line from this point back to the origin.