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