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