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