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