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