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