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