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