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