One vertex per element, one color per generator, with an edge from x to x·s.
(1,2,4,3)(5,6)(7,17)(8,23)(9,28)(10,31)(11,16)(12,21)(13,27)(14,29)(15,18)(19,38)(20,46)(22,40)(24,52)(25,55)(26,36)(30,59)(32,45)(33,48)(34,41)(35,61)(37,43)(39,47)(42,51)(44,65)(49,54)(50,56)(53,60)(57,58)(62,66)(63,64)(67,68)(1,3,4,2)(5,7,18,41,11,22,10,21)(6,12,31,40,16,34,15,17)(8,24,42,45,27,19,26,54)(9,20,43,64,30,48,29,47)(13,32,51,52,23,49,36,38)(14,33,59,63,37,46,28,39)(25,53,61,66,57,44,56,68)(35,60,55,67,50,65,58,62)(5,8)(6,13,16,23)(7,19,22,24)(9,25)(10,26)(11,27)(12,32)(14,35,37,50)(15,36,31,51)(17,38)(18,42)(20,44,48,53)(21,45,41,54)(28,58,59,55)(29,56)(30,57)(33,60)(34,49)(39,62)(40,52)(43,61)(46,65)(47,66,64,68)(63,67)(5,9,18,43,11,30,10,29)(6,14,31,59,16,37,15,28)(7,20,41,64,22,48,21,47)(8,25,42,61,27,57,26,56)(12,33,40,63,34,46,17,39)(13,35,51,55,23,50,36,58)(19,44,54,68,24,53,45,66)(32,60,52,67,49,65,38,62)A Cayley diagram is a choice, not a fact about the group. Another drawing of this group — in a book, or on a different generating set — may look nothing like this one.