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