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