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