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