Silly Symphonies was a separate movie series created by Walt Disney to produce music themed cartoon shorts that weren’t tied to the hugely popular Mickey Mouse, though they were “presented” by him. The series was more ambitious than the Mickey Mouse shorts and was the first to feature the expensive technicolor process in 1933.
The huge success of the Mickey Mouse shorts led Roy Disney to discourage his brother from using the expensive technicolor process to produce them; after all, Mickey Mouse was popular enough, why spend the extra money to make them? Walt Disney, however, was never willing to settle for second best, so in 1935, he was finally able to convince Roy to let him begin producing the Mickey shorts in color. The first was Mickey’s Band Concert.