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