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