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