Why are airplanes alwayes painted white?

There are several reasons for this

• Thermal utility

The white color reflects sunlight and reflects most of the light falling on it.
Unlike the rest of the colors that absorb the light falling on it and this leads to the heat of the fuselage, which is to avoid.

• Overlay coating = larger weight = more fuel expense = larger operating costs

• The white color does not fade or pull

• The resale value is higher than others colors
  The white-painted plane has a value to be resold beyond the value of the colored aircraft.

Most corporate jets are chartered planes, so the owners prefer white so they do not need to re-paint. They only have to change the company's old name and put a name and logo for the new company.

source : https://engineeringinsider.org/airplanes-painted-white/ & https://mechanicalsphere.blogspot.com.eg/2018/02/know-airplanes-are-mostly-painted-in.html