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