Commercial planes are generally white for these reasons: white color provides a thermal advantage, helps in the easier inspection of cracks and dents on the fuselage, and is also cost-effective. White planes also tend to have a higher resale value than colored ones.

Decorative paintings are expensive
Cost can run anywhere from $50K to $200K per plane. The 2-3 weeks of time required for such paint jobs will cause a loss of revenue for that period.

More paint= More weight= More fuel = More operating costs
The paint on a fully painted 747 will weigh more than 250 kg, while polished skin will just weigh 25 kg. EasyJet Airlines was able to reduce 2% of their operating costs by just repainting their planes with new thinner aerodynamic paints. When your annual fuel bill is $1.2 billion USD, then that 2% can mean a savings of $22.4 million USD. Suddenly a coating becomes interesting, doesn’t it?

Colorful Airplanes have low resale value.
Painting an aircraft in a color other than white can negatively affect its resale value as the buyer will have to repaint the plane which will further add more weight to the plane.

The airliners which purchase brand new planes instead of leasing are almost always purchasing by using huge long-term loans. This is a huge investment in a competitive market. They may themselves want to sell or lease their planes if things don’t go well.

White has some significant thermal advantages over color.
A white object reflects all wavelengths of light, so the light is not converted into heat, while a colored object absorbs more wavelengths of light and converts them into heat, so the object gets warm.

White is a nice, neutral base color.
Artists typically start out with a white canvas or white paper – it’s a color associated with “blank” and “clean”. Starting with a white base coat allows the airline’s marketing department to paint whatever livery they want on their flying billboards.

White doesn’t fade. 
An average airliner will have several paint jobs during its service life, but the longer you can go between having to repaint the plane the better, and if you don’t have to worry about the paint fading and looking old for a good long while you can stretch the time between paint jobs without having your passengers start making snide comments about your fleet of flying hoopties.