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