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