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