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