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