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