At the login screen of some machines you will see a small text box in the top right hand corner which allows you to adjust the resolution of your X display. Figure 4.1 is an example of what the text box looks like. Some resolution selection boxes offer higher bit depth than the one shown.
Applications use several colours when they are displayed on your screen. If you select 8-bit colour you will have 256 colours available. Firefox, for example, can use many colours and you may find that running a text editor like nedit at the same time will force it to have a white background as opposed to grey. This is because Firefox has grabbed the colours it needs to display its window first. Further applications then use what they can. If you use the 16-bit colour option (or higher) before you log in to a machine, this will not occur.
It is strongly recommended that you select 16-bit colour (or higher) if you are using the WindowMaker or KDE window managers. Being more detailed than the default fluxbox window manager they tend to use many colours. For more information on window managers see section 4.6 on page .Loc Van Huynh 2007-03-15