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