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)(26,30)(27,33)(31,37)(34,38) involution — undirected(9,11,13,19)(10,14,16,17)(12,18,20,24)(15,21,22,23)(26,31)(27,34)(29,36)(30,37)(33,38)(39,40)(1,3,5,4)(2,6,7,8)(9,12,13,20)(10,15,16,22)(11,18,19,24)(14,21,17,23)(25,26)(27,35)(28,30)(29,37)(31,36)(32,33)(34,40)(38,39)(10,16)(14,17)(15,22)(21,23)(27,33)(32,35)(34,38)(39,40) involution — undirected(1,4,5,3)(2,6,7,8)(11,19)(14,17)(18,24)(21,23)(25,27,28,33)(26,32,30,35)(29,38,36,34)(31,39,37,40)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.