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