Each user can change the Background color, Menu Bar color, or Panel Header color.
To use the color picker:
Click on your name or picture to display the User Preferences menu.
Select User Preferences.
Click in the colored Background, Menu Bar or Panel Header box.
Click to select the desired color from the standard color palette.
To select a custom color instead of a standard color:
Drag the color slider to the desired color family, then drag the color selector dot to the desired color intensity.
Click Choose.