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