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