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