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