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