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