For each X11 screen, one of the exported visuals for the screen is designated the default visual. The default visual is the visual assigned to the screen's root window, and this visual is the visual that most applications use to create their windows. When a client application starts, its windows are assigned the default visual unless the application specifies a different visual.
The built-in default visual is the visual hard-coded in the Solaris X server. For each screen, there is a default visual that depends on the characteristics of the display device for that screen. This is the default visual unless you specify a different default visual when you run openwin(1).
Users can change the default visual that window server advertises in the connection block. One reason for this is to force client programs that cannot run in the default visual to run in a specific visual. For example, on a 24-bit device that has the TrueColor visual as its default visual, an application that cannot run with 24-bit color may run on a PseudoColor visual.
For developers on multi-depth devices, changing the default visual is a useful way to test that your application works in different configurations. For information on how to change the default visual, see the xsun(1) man page. The default visual and the list of supported visuals exported by the server can be examined from X11 using XGetVisualInfo(3).