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