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