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