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