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