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