Why are umbrellas mostly black in color?
It's just because black colour has an advanced ability to absorb heat radiations much better and faster than any other colour. Then you might ask why does then we use it at sunshine to prevent body from heat. No surprise to your question it's because at the same time black is able to liberate back the absorbed heat at a faster rate. If you doubts this then you doubt about one more thing that why does most of the umbrellas are made silverish inside it. The answer to this is that black expells heat in all directions so in order to prevent heat entering inside the umbrella it is painted silverish inside as silver acts as a mirror, so it just reflects the heat back out to the umbrella. So we finds much cool inside with a silver coated umbrella than a black one.
The studies regarding this matter has founded that if we use black umbrellas in summer we will feel more hot. because the black colour absorbs more heat that other colours. so it is suggested to use bleck umbrellas in winter due to that black absorbs all amount of energy from the sunlight in winter. it makes us more comfortable with it.
There are many colors and patterns of umbrellas, but I would guess the reason that they are often black is that it is a neutral color and matches almost anything. But i disagree with that the umbrella is always black,since umbrella is the object used during both summer and rainy seasons, so in summer black is the only colour that prevents penetrating heat, so from the past umbrella is always black.