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