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