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