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