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