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