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