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