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