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