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