Provided by: x11-xserver-utils_7.7+2ubuntu1_amd64
showrgb - display an rgb color-name database
showrgb [ database ]
The showrgb program reads an rgb color-name database from a text file and converts it back to source form, printing the result to standard output. The default database is the one that X was built with, and may be overridden on the command line. Specify the database name without the .txt, .pag or .dir suffix.
/usr/share/X11/rgb default database.