The flag of Germany or Bundesflagge was proclaimed by the Federal constitution of 1949. It was the after World War II constitution which also demanded another symbols and another Germany flag. A totally new flag was not invented as there was a good candidate -the black-red-gold tricolor Bundesflagge originated back in 1840s after defeat of Napoleon. At that time black-red-gold became symbols of liberalism and neglecting a conservative order.
About the origin of the colors and symbols there are still some argues.
But the main version of the origin says that the Volunteer Free Corps of university students and teachers had a uniform of a black clothing and red facings with bronze-gold buttons.
In short regardless the real origin of the colors the main idea they convey is the spirit of liberalism.
Another interesting fact that German Democratic Republic or GDR had also a similar flag but with a different sign in the center which symbolized that the country belonged to farmers and workers or peasants and proletariat.
After unification of the FRG and GDR the flag of Germany had the same look.
Also could be of interest a poetical interpretation of the flag colors:
der Schwärze der Knechtschaft durch blutige Schlachten ans goldene Licht der
Freiheit" or "Out of the darkness (black) of
servitude, through bloody (red) battles to the golden (gold) light of
freedom". Any person can use it for
himself personally as well-to get rid of inner servant or slave through
personal development and reaching finally freedom. Germans were always famous
for being philosophers. Not all of them, of course, but it is an interesting
approach to the Germany flag colors.
Lately National flag of Germany was very often used in Berlin because of the Football World Cup 2014. A strong waive of patriotism was seen everywhere in Berlin. Tricolor you could see everywhere. Cars decorated with little flags. Germany flags on balconies. Kids and adults wearing clothing and accessories containing Germany flag colors.
And when a victorious German football team returned with triumph to Berlin the center of the capital was full of people carrying flags and having something with tricolor. Happy people and also proud. They came to express their admiration and thankfulness to the team. Germans are crazy about football. Every lost play is a tragedy and every won play is joy and fireworks which they make from balconies and other places which they can immediately reach and get back to continue enjoying a game.
But such pictures are not so often. Usually under normal circumstances Berliners do not wear tricolor. The only reason is football. For the sake of football they magically find Germany flags and fireworks. They become real patriots. Streets are almost empty when German football team plays.
Tricolor is not the only flag you can see visiting authorities and some institutions in Berlin. It is usually together with the EC flag and the flag of Berlin. A current situation is demanding three flags.