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