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