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