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)(11,18)(12,17)(13,22)(14,16)(15,19)(20,24)(21,23)(25,26)(27,30,34,37)(28,32)(29,31)(33,38,35,40)(36,39)(2,5)(6,7)(9,11,12,21,14,20,13,19)(10,15,22,24,16,23,17,18)(25,27,29,34)(26,30)(28,35,36,33)(31,37)(32,40)(38,39)(1,3,4,8)(2,6,5,7)(10,16)(15,23)(17,22)(18,24)(26,31)(28,36)(30,37)(33,35)(9,12,14,13)(10,17,16,22)(11,19,20,21)(15,24,23,18)(25,28,29,36)(26,32,31,39)(27,33,34,35)(30,38,37,40)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.