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