One vertex per element, one color per generator, with an edge from x to x·s.
(2,6)(3,4)(7,8)(9,10)(11,18)(12,15)(13,17)(14,23)(16,21)(19,20)(22,24)(25,26)(27,30)(28,31)(29,32)(33,39)(34,37)(35,38)(36,40) involution — undirected(3,4)(6,8)(9,11,15,22)(10,16,12,19)(13,21,14,20)(17,24,23,18)(25,27)(26,30)(28,33)(29,34)(31,36)(32,37)(35,40)(38,39)(1,2)(3,6)(4,8)(5,7)(9,12,15,10)(11,19,22,16)(13,17,14,23)(18,21,24,20)(25,28)(26,31)(27,33)(29,35)(30,36)(32,38)(34,40)(37,39)(1,3,5,4)(2,6,7,8)(9,13,15,14)(10,17,12,23)(11,20,22,21)(16,18,19,24)(26,32)(30,37)(31,38)(36,39)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.