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