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