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