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