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