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