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