cc [ flag ... ] file ... -lXext [ library ... ] #include <X11/extensions/Xcup.h>
The XcupGetReservedColormapEntries function returns a list of colormap entries (pixels) that are reserved by the system. This list will, at a minimum, contain entries for the BlackPixel and WhitePixel of the specified screen. Use XFree to free colors_out.
To minimize colormap flash, an application which installs its own private colormap should query the special colors by calling XCupGetReservedColormapEntries, and can then store those entries (in the proper location) in its private colormap using XCupStoreColors.