You have seen in for yourselves, all passenger airplanes have logos and inscriptions, but always the background is white.
Yes, some of the planes come in other colors and editions, but 99% of all passenger airplanes are white. There are several reasons, but normally, the most important reason is security.
When the surface of the aircraft is white, it is way easier to spot cracks, leaks of oil and many other problems that can occur if the plane was defective. And when problems are visible they are easily resolved.
Also, white color reflects best the light and the heat, which is quite important in reducing the heating of the plane. In addition, white is one of those most easily observed in the sky, in the event of a collision or in bad weather. On top of all, white is the only color that never fades away like any other color.
Of course, there are also economic reasons for painting the aircraft is long and fairly expensive process, so in the mentioned advantages of white, there is really no point to use a different color. Painting usually takes between two days and two weeks, depending on the budget of the airline. Lastly, colored planes are harder later sold to other companies, which may have been among the main reasons why to go white.