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