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