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