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