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