7 Color in the Window Tool Kit

7.3 Color checklist

• Does your display support graphics? If your display does not support graphics, you cannot initialize the Window Took Kit or see color. Your display supports graphics if the functionwindows-available-p returns a non-nil value.

• Is the window system initialized? Until the window system is initialized, colors cannot be displayed. The window system is initialized if the function root-viewport returns a non-nil value.

• Does your display support color? Your display must support color for color operations to be effective. Your display supports color if the third value returned by windows-available-p, which is the depth of your display, is greater than 1 or if color-available-p returns a non-nil value.

• Have you registered any colors? The colors'BLACK and'WHITE are the only colors that are automatically registered upon initialization. Failure to register colors is the most common reason for not seeing color. To see which colors are registered, invoke the function print-color-registry. To register primary colors automatically, use the functionsetup-color-library.

• Have you performed any operations using registered colors? You must specify colors as arguments to functions that accept registered colors.

• Are your output windows of the same depth returned by the function display-depth? If the window that you are sending output to is of depth 1, you cannot see any colors in that window. By default, all windows and bitmaps are of depth 1, and color output to depth 1 bitmaps shows as'BLACK. To find the depth of your window, use the functionbitmap-depth with the window as an argument.

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