In computing, a theme is a preset package containing graphical appearance details, used to customize the look and feel

Look and feel

In software design, look and feel is a term used in respect of a graphical user interface and comprises aspects of its design, including elements such as colors, shapes, layout, and typefaces , as well as the behavior of dynamic elements such as buttons, boxes, and menus...

 of (typically) an operating system, widget set or window manager

Window manager

A window manager is system software that controls the placement and appearance of windows within a windowing system in a graphical user interface. Most window managers are designed to help provide a desktop environment...

.

Graphics themes for individual applications are often referred to as skins

Skin (computing)

In computing, a skin is a custom graphical appearance achieved by the use of a graphical user interface that can be applied to specific software and websites to suit the purpose, topic, or tastes of different users....

, and the words are often used equivalently, the primary difference being one of scope.

Usage

Themes are often used to change the appearance of a wide range of things at once, which makes them much less granular

Granularity

Granularity is the extent to which a system is broken down into small parts, either the system itself or its description or observation. It is the "extent to which a larger entity is subdivided...

 than allowing the user to set each option individually. For example, you might want the window-borders from a particular theme, but installing it would also alter your desktop background.

One method for dealing with this is to allow the user to select which parts of the theme they want to load, for example in Windows 98, you could load the background and screensaver from a theme, but leave your icons and sounds untouched.

Themed systems

• dhex
  Dhex
  dhex is a hex editor with a diff mode. It is intended for low-level analysis of large binary files.Based on ncurses, it can run on any number of systems and scenarios.- Features :...
  
   uses themes to be usable under different terminal emulations.
• IceWM
  IceWM
  IceWM is a stacking window manager for the X Window System graphical infrastructure, written by Marko Maček. It was coded from scratch in C++ and is released under the terms of the GNU Lesser General Public License...
  
   uses themes to customise its taskbar, window borders, and time format.
• Desktop Architect
  Desktop Architect
  Desktop Architect is a third-party replacement for the Desktop Themes control panel in Windows 95, 98, ME and 2000. It is also fully compatible with Windows XP and Vista. However, in Vista, the startup sound does not work, and the Network Neighborhood icon has to be changed manually...
  
   allows users to customize, create, and manage and apply their own themes.
• GNOME
  GNOME
  GNOME is a desktop environment and graphical user interface that runs on top of a computer operating system. It is composed entirely of free and open source software...
  
   and KDE
  KDE
  KDE is an international free software community producing an integrated set of cross-platform applications designed to run on Linux, FreeBSD, Microsoft Windows, Solaris and Mac OS X systems...
  
   use two independent sets of themes: one to alter the appearance of buttons, scrollbars, list elements, (for example to specify glassy-effect pushbuttons or square ones), and another theme to customise the appearance of windows (for example, window borders and title bars). One popular example is Clearlooks
  Clearlooks
  Clearlooks is a theme engine for GTK+, the main widget toolkit used by the GNOME desktop environment. It is based on Red Hat's Bluecurve theme. The theme engine draws the actual widgets, and can be configured with 'themes' that invoke the theme engine with different configurations. It is the...
  
  .
• Mac OS
  Mac OS
  Mac OS is a series of graphical user interface-based operating systems developed by Apple Inc. for their Macintosh line of computer systems. The Macintosh user experience is credited with popularizing the graphical user interface...
  
   is themeable through third party applications, such as Kaleidoscope and ShapeShifter
  ShapeShifter
  ShapeShifter is an Application Enhancer plugin for Mac OS X developed by Unsanity that allows the user to make system-wide modifications to the appearance of the operating system's graphical interface by applying GUI skins through “injection” into running code and without modifying system files,...
  
  . Apple had planned to release system themes in version 8 of their OS, but they were removed at the last minute.
• WindowMaker can store colors for icons, menus, and window-borders in a theme, but this is independent of the wallpaper settings (and WindowMaker has no taskbar to customise)
• Windows 98
  Windows 98
  Windows 98 is a graphical operating system by Microsoft. It is the second major release in the Windows 9x line of operating systems. It was released to manufacturing on 15 May 1998 and to retail on 25 June 1998. Windows 98 is the successor to Windows 95. Like its predecessor, it is a hybrid...
  
   and Windows Me
  Windows Me
  Windows Millennium Edition, or Windows Me , is a graphical operating system released on September 14, 2000 by Microsoft, and was the last operating system released in the Windows 9x series. Support for Windows Me ended on July 11, 2006....
  
   came with themes such as "nature", "space", etc. which contained desktop backgrounds, icons
  Icon (computing)
  A computer icon is a pictogram displayed on a computer screen and used to navigate a computer system or mobile device. The icon itself is a small picture or symbol serving as a quick, intuitive representation of a software tool, function or a data file accessible on the system. It functions as an...
  
  , sounds, colors, and cursors. This was also provided by Plus! for Windows 95 and the theme program also in the VALUEADD for Office 97.
• Windows XP
  Windows XP
  Windows XP is an operating system produced by Microsoft for use on personal computers, including home and business desktops, laptops and media centers. First released to computer manufacturers on August 24, 2001, it is the second most popular version of Windows, based on installed user base...
  
   introduced several new themes, including Luna
  Luna (theme)
  Themes customize the appearance of the Windows operating system without changing its functionality ....
  
   and Royale, which were both very different from the "Classic" look in previous versions of Windows.
• Windows Vista
  Windows Vista
  Windows Vista is an operating system released in several variations developed by Microsoft for use on personal computers, including home and business desktops, laptops, tablet PCs, and media center PCs...
  
   introduced a new theme called Aero
  Windows Aero
  Windows Aero is the graphical user interface and the default theme in most editions of Windows Vista and Windows 7, operating systems released by Microsoft. It is also available in Windows Server 2008, but is not enabled by default. Its name is a backronym for Authentic, Energetic, Reflective and...
  
   which aims to give the user a cleaner and sleeker look to windows. Windows 7 also uses a modified version of Aero by default.
• Java
  Java (programming language)
  Java is a programming language originally developed by James Gosling at Sun Microsystems and released in 1995 as a core component of Sun Microsystems' Java platform. The language derives much of its syntax from C and C++ but has a simpler object model and fewer low-level facilities...
  
  programs can select from several themes, controlling the appearance of the application.