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