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