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