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)(11,17)(12,16)(13,15)(14,19)(18,24)(20,22)(21,23) involution — undirected(9,11,13,19)(10,14,15,17)(12,20,21,18)(16,24,23,22)(25,26,31,34)(27,35,37,38)(28,33,30,39)(29,36,32,40)(2,5)(6,8)(25,27,31,37)(26,32,34,29)(28,36,30,40)(33,38,39,35)(1,3,4,7)(2,6,5,8)(10,15)(14,17)(16,23)(22,24)(25,28,31,30)(26,33,34,39)(27,36,37,40)(29,35,32,38)(9,12,13,21)(10,16,15,23)(11,18,19,20)(14,22,17,24)(25,29,31,32)(26,27,34,37)(28,38,30,35)(33,40,39,36)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.