This illustration explains the
Blutschutzgesetz: In general, the light (or the cross) symbols stand for German-blooded, the dark symbols for Jew. In general: No restriction if both people are German-blooded; If one of them is Quarter-Jew (
Mischling 2. Grades) also no problem; Half-Jews need a special permission to marry people of German blood (no such permissions were actually given); People that are more than half-Jew are not permitted to marry (or have sex with) German-blooded people