The main reason why every other plane is white has a lot to do with Thermal science. As per the basic science we have read in school, white colour reflects the sunlight, hence reducing the temperature inside the cabin, which in return results in lesser usage of fuel in cooling the craft, hence more fuel saving. Also, white colour shields the plane’s plastic parts including the nose cone and composite materials from the sun, which can be a big safety hazard otherwise.
The next big reason for airlines to opt for white aircraft over other colours is the fact that white is the most economical paint. An average size single-aisle aeroplane like the Airbus A320 or Boeing 737 uses 65 gallons (245 litres) of paint for a single coat. Also, aeroplanes need periodic maintenance to maintain the glossy effect which in turn improves aerodynamics. So it’s wise to use the cheapest and easy to maintain colour, which turns out to be white.
Lastly the resale value. The airline industry works on lease model and airline carriers don’t directly buy the aircrafts from companies like Airbus or Boeing. It has been seen that white planes sell quicker than colored or unpainted planes. Buyers prefer unmarked, without livery white planes so that they can customize accordingly.