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