Originally Posted by Wikipedia

Brown
The brown color that UPS uses on its vehicles and uniforms is called UPS Brown, which was chosen because it is the same color that was used on Pullman railroad sleeper cars and was seen as professional and elegant. The brown color hides dirt well and was inconspicuous. This color is often erroneously referred to as Pantone color 0607298, but this is not a valid Pantone number.[6] The department stores UPS did deliveries for did not want to call attention to the fact that UPS was delivering their furniture, rather than their own delivery people. The color UPS Brown is trademark, which prevents other delivery companies from using it as part of their brand.