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