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