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