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