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