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