Henry Ford famously said:
"Any customer can have a car painted any color that he wants so long as it is black."
He actually had a good reason: black paint dried quickly, thus allowing him to operate the assembly line at a higher speed.
Today, you can have your car in a large number of standard colors. You can have your web browser in any color you want—Firefox now offers more than 35,000 "personas" with different colors and images.
You probably don't want to offer your enterprise application in thousands of color schemes, but you do want to build a visually attractive application that matches the graphical identity used by your organization. If your application is going to be used by several different groups of users, for example, if it is going to be deployed to multiple customers, you want it to be easy to change the appearance of the application.