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