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