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