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