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