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