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