property, standard colormaps can be used by different applications. The creation of colormaps is regulated by the ICCCM convention. Standard colormaps are regulated by the ICCCM and by the Xlib specification. A part of the X colour system is the X Color Management System (xcms). This system was introduced with X11R6 Release 5 in 1991. This system consists of several additional features in xlib, found in the Xcms* series of functions. This system defines device independent color schemes which can be converted into device dependent RGB systems. The system consists of the xlib Xcms* functions and as well the X Device Color Characterization Convention (XDCCC) which describes how to convert the various device independent colour systems into device dependent RGB colour systems. This system supports the CIEXYZ, xyY, CIELUV and CIELAB and as well the TekHVC colour systems. , Atoms Atoms are 32-bit integers representing strings. The protocol designers introduced atoms because they represent strings in a short and fixed size: while a string may be arbitrarily long, an atom is always a 32-bit integer. Atom brevity was exploited by mandating their use in the kinds of packets that are likely to be sent many times with the same strings; this results in a more efficient use of the network. The fixed size of atoms was exploited by specifying a fixed size for events, namely 32 bytes: fixed-size packets can contain atoms, while they cannot contain long strings. Precisely, atoms are identifiers of strings stored in the server. They are similar to the identifiers of resources (Windows, Pixmaps, etc.) but differ from them in two ways. First, the identifiers of atoms are chosen by the server, not by the client. In other words, when a client requests the creation of a new atom, it only sends the server the string to be stored, not its identifier; this identifier is chosen by the server and sent back as a reply to the client. The second important difference between resources and atoms is that atoms are not associated with clients. Once created, an atom survives until the server quits or resets (this is not the default behavior of resources). Atoms are identifiers and are therefore unique. However, an atom and a resource identifier can coincide. The string associated with an atom is called the atom name. The name of an atom cannot be changed after creation, and no two atoms can have