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