Commodore's Graphicraft program uses a similar chunk "CCRT" (for Color Cycling Range and Timing). This chunk contains a CycleInfo structure. typedef struct { WORD direction; /* 0 = don't cycle. 1 = cycle forwards */ /* (1, 2, 3). -1 = cycle backwards (3, 2, 1) */ UBYTE start, end; /* lower and upper color registers selected */ LONG seconds; /* # seconds between changing colors plus... */ LONG microseconds; /* # microseconds between changing colors */ WORD pad; /* reserved for future use; store 0 here */ } CycleInfo; This is very similar to a CRNG chunk. A program would probably only use one of these two methods of expressing color cycle data, new programs should use CRNG. You could write out both if you want to communicate this information to both Deluxe Paint and Graphicraft.