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