One vertex per element, one color per generator, with an edge from x to x·s.
(1,2,4,3)(6,13)(7,18)(8,11)(9,27)(10,28)(14,35)(15,40)(16,43)(17,24)(19,30)(20,47)(21,54)(22,44)(23,48)(25,50)(26,31)(29,51)(32,37)(33,41)(36,56)(38,64)(39,63)(42,58)(45,46)(49,53)(52,60)(55,66)(59,62)(61,65)(67,68)(1,3,4,2)(5,6)(7,14)(8,24)(9,15)(10,16)(11,13)(12,17)(18,37)(19,36)(20,52)(21,38)(22,32)(23,39)(25,56)(26,57)(27,41)(28,34)(29,33)(30,42)(31,43)(35,47)(40,50)(44,63)(45,59)(46,65)(48,60)(49,64)(51,58)(53,67)(54,62)(55,61)(66,68)(5,7,19,49,10,21,29,47,8,20,50,54,26,53,9,18,12,23,27,46,31,55,25,44,11,22,51,66,28,45,30,48)(6,14,36,64,16,38,33,35,24,52,40,62,57,67,15,37,17,39,41,65,43,61,56,63,13,32,58,68,34,59,42,60)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.