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