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