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