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