I think it would be safe to assume that Microsoft calls a unique collection of display properties (icons, colors, background, and so on), mouse cursors, and sounds a theme because it has thematic intent, meaning the theme uses a unifying topic or subject that then dictates how each of the theme elements looks.
For example, if you create a Windows theme based on your team sport, you would want the color scheme to use your favorite team's colors (or be complementary to the team's colors), have a background that shows the team (or your favorite player in action), and then have icons and cursors that match the overall concept of the theme. Take a look at the simple hockey theme shown in Figure 4.2.
Figure 4.2. Theme elements typically adhere to a unifying subject.
The hockey theme uses custom icons related to the game (that's Lord Stanleythe Stanley of the Stanley Cupas the Empty Recycle Bin icon). Custom mouse pointers are also used (the default mouse pointer has a hockey puck motif and is shown on the desktop). It also uses a photo of Vincent Lecavalier (of the 2004 Stanley Cup Champion Tampa Bay Lightning). The photo used for the background was selected because it provided some light-colored areas that serve well as places to park the desktop icons (and make it easy to see the icons). The color scheme selected was designed to complement (rather than clash with) the background.
Although your theme should have some sort of unifying topic or subject that influences the various theme elements, I certainly do not want to dampen your personal artistic fire. Themes can be quite abstract, as can art, so the creation of your theme can be an artistic journey where you determine the connection (or non-connection) between the various theme elements. As long as you are happy with the theme and enjoy using it to dress up the Windows environment, I would say that the theme is a success.
In terms of color schemes, fonts, and backgrounds, you do want to be somewhat practical, however, in terms of overall usability. The Windows environment is where you use various applications and utilities. Therefore, you don't want to create an environment in which the background, colors, or fonts make it difficult for you to function and you have problems reading window titles or can't really see the desktop icons because of an extremely busy background.
To some extent, creating themes (and visual styles and skins, which we discuss later in the book) is a trial-and-error process. When a certain element of the theme looks good, you keep it and move on to the next element. When an element doesn't work, you can modify it.
Let's walk through the process of creating a theme. We will start with the display property elements of the theme, such as the desktop icons, color scheme, and desktop background of the new theme.