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)(27,33)(28,37)(29,34)(30,39)(31,35)(32,36)(38,40) involution — undirected(1,3)(2,5)(4,7)(6,8)(9,11)(10,14)(12,18)(13,19)(15,21)(16,17)(20,24)(22,23)(27,28)(32,40)(33,37)(36,38) involution — undirected(3,7)(5,8)(9,12,13,20)(10,15,16,22)(11,18,19,24)(14,21,17,23)(25,27,31,28)(26,32,35,40)(29,36,30,38)(33,34,37,39)(2,6)(3,7)(11,19)(14,17)(18,24)(21,23)(25,28,31,27)(26,33,35,37)(29,36,30,38)(32,34,40,39)(3,7)(5,8)(10,16)(14,17)(15,22)(21,23)(25,29,31,30)(26,34,35,39)(27,36,28,38)(32,37,40,33)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.