The colours of the flag
Black represents the world darkness and ignorance as well as the aspiration to light and knowledge, source of freedom.
Yellow symbolizes the golden sun, the heavenly essence whose beam acts as a communication channel between the celestial and bright world and the terrestrial and obscure world. As the median colour of the rainbow spectrum, it characterizes the balance between the extremes, purple and red, and symbolizes the soundness at the base of justice.
Red, located at the top of the rainbow, a real bridge between Heaven and Earth, symbolizes the power of the Emperors, Kings, Princes and, why not, Heads of State, illuminated by the light of the heavenly beam. This is why, Emperors of ancient times were dressed in yellow or red.
Curiously, the order of the colours from the terrestrial world towards the celestial world is top-down (black at the top, red in the middle and yellow at the bottom). This is due to the double meaning of black. If black characterizes the darkness of the terrestrial world, it also symbolizes the invisible world beyond the celestial world, at the source of all things and colours in particular. Consequently, black can only stand at the top of the flag pole.
Note in passing that the German flag has similar colours to those of the Kingdom of Belgium and that the Austrian flag also displays an eagle on its coat of arms.
The coat of arms
The coat of arms in the middle of the State flag is composed of a black eagle, with red beak and claws and deployed wings on a (golden) yellow shield.
Flying to the highest level in the sky, the eagle is the king of birds, the only one able to fix the sun without burning its eyes. It alone has a direct access to the celestial light intended to enlighten the beings here below. It has become a symbol of the Sun in virtually all civilizations, especially Greek and Roman. As the Imperial emblem of Caesar, it inspired Charlemagne on the occasion of his coronation in the year 800. The new Emperor chose the eagle as a symbol of the immense territory conquered of high fight and called to become the Holy Roman German Empire.
In the Middle Ages, the Germanic crusaders wore an eagle on their flags and shields. Around the 15th century, the eagle became bicephalous. It was less a matter of duplicating the head of the Kingdom or Empire than to strengthen the power of the royalty, to make it a true imperial sovereignty, the King of the kings. This eagle particularly faced another eagle with a single head, the Napoleonic eagle, eager to fight the Germanic Empire.
During the course of the 19th century, the eagle became the emblem of the quest for the unification of the country. The unity carried out, Bismarck made it the national symbol with a single head turned toward the pole and decorated with the attributes of the Empire: a crown, a chain and a shield. The Weimar Republic deprived it of its imperial attributes and the Third Reich represented it with fully deployed wings. The new Federal Republic which emerged from the rubble in 1950 took over the eagle as emblem. An eagle making a clean sweep of the nazi period and surprisingly resembling to the one of the Weimar Republic.
The experience of the Second World War and especially of the Reunification was decisive regarding the relationships between the German society and the national symbols. The identification of the eagle to the early imperialist views reached its climax and put shame on the symbol. The Reunification create a deep-rooted feeling of unity around the three colours: black, red and (golden) yellow, particularly apparent in the flags of the GDR with a hole in the middle. The young generations claimed a unity visible in the common colours of the flags of the two countries. The eagle lost its authority over the temporal power for the benefit of the three colours.